Testing a Phone Before You Buy and Before You List: IMEI, Locks, and Function Checks

Five minutes before money moves saves the deal.

Every flip-killing failure on a used phone is detectable in person before payment. A blacklisted IMEI. An active iCloud Activation Lock. A Google FRP lock the seller's "factory reset" never cleared. A swollen battery hiding under a curved display. An "Unknown Part" battery that no longer reports a percentage. Sellers who lose money on used phones lose it in the same five places — and the entire defensive checklist runs in under fifteen minutes per device. This spoke is that checklist: what to dial, what to read, what to watch boot, and what to do when one of the checks fails.

Get the IMEI before you commit to a price.

The IMEI (International Mobile Equipment Identity) is the 15-digit serial that anchors every other identity check. It is non-negotiable. A seller who will not share an IMEI before meeting is selling a problem.

Three places to read it

• Dial *#06# on the device dialer — works on every modern iPhone and Android, displays the IMEI on screen immediately.
• Settings > General > About (iPhone) or Settings > About Phone (Android) — scroll to the IMEI field.
• SIM tray engraving on most modern iPhones, and the retail box on any device that still has original packaging.

Confirm the numbers match across all three. If the dialer IMEI does not match the SIM-tray engraving or the box, the board has been swapped or the housing replaced — walk. Dual-SIM iPhones from XS forward have two IMEIs; record both.

Two free blacklist checks — run both

One check is not enough. Each free service pulls from a slightly different slice of the carrier and registry data.

• CTIA Stolen Phone Checker (stolenphonechecker.org). Powered by the GSMA Device Check service that carriers and law enforcement use. Returns a binary result: green (not reported) or red (reported lost or stolen). About 5 free queries per day for US consumers (re-verify before launch). If this returns red, no other diagnostic matters.
• Swappa IMEI Check (swappa.com/imei). Free to the public, 10 checks per 24 hours (re-verify before launch). Checks against the GSMA registry, returns allowlist/blocklist status, device model, and current market value. Swappa uses this in its own listing review.

Cross-checking surfaces gaps. CTIA is strongest on US-carrier-reported lost/stolen. Swappa adds device model identification and pricing context. Neither check is a financing-balance check on its own — that is a separate carrier-portal lookup or an in-person $0-balance screenshot from the seller's carrier app.

What the IMEI does not tell you

• Whether an installment-plan (EIP) or lease balance is still owed
• Whether iCloud Activation Lock is currently active
• Whether Google FRP is currently active
• Whether the device is carrier-locked, and to which carrier

Each of these is a separate check in the sections below.

Carrier lock and unpaid balance are two different conditions.

Most new flippers conflate them. They are different problems with different fixes, and one of them — the unpaid balance — is the silent killer of an otherwise clean phone.

Carrier lock — how to read it

• iPhone: Settings > General > About > Carrier Lock. "No SIM restrictions" means unlocked; any carrier name means locked to that carrier.
• Samsung released before September 1, 2025: Settings > About Phone > Software Information > Service Provider Software Version. A suffix like ATT/ATT indicates the originating carrier.
• Samsung released on or after September 1, 2025: Settings > Connections > More Connection Settings > Network Lock Status.
• Universal physical test: insert a SIM from a different carrier. If the phone connects and allows calls or data, it is unlocked. If it prompts for an unlock code or rejects the SIM, it is locked.

A locked phone is not automatically a deal-breaker. It is a discount input. Many buyers shop for unlocked devices, but the locked-to-original-carrier listing has its own audience at a lower price.

Financing / unpaid balance — the silent killer

A phone can read "unlocked" in its own settings — because a carrier pushed an automatic unlock — while still carrying an unpaid installment balance. The moment the seller skips the next bill, that balance triggers a blacklist. The device is clean on your day of purchase and bricked thirty days later.

• AT&T: the device unlock portal (att.com/deviceunlock) returns "all of the installment payments have not been paid" if a balance remains. AT&T requires roughly 60+ days since purchase, installment balance at zero, account current, and not reported lost or stolen (re-verify before launch).
• T-Mobile: the IMEI compatibility checker and the My T-Mobile portal both reflect unlock eligibility. T-Mobile postpaid typically requires about 40 days of active service on the requesting line plus all financing satisfied; prepaid generally requires roughly 365 days of active service or more than $100 in refills (re-verify before launch).
• Verizon: devices unlock automatically when purchased at full retail or when the financing balance hits zero. Calling 800-922-0204 or dialing *611 confirms status. Prepaid typically requires roughly 365 days of paid active service (re-verify before launch). Verizon states it will not re-lock once unlocked.

The cleanest way to settle this in person: ask the seller to open their carrier app (My Verizon, myAT&T, T-Mobile) and show the device summary screen — $0 device balance, account current. A receipt proves the phone existed at the carrier; only the carrier-app screenshot proves the payoff.

iCloud lock is unrecoverable without the original owner.

Activation Lock is Apple's kill-switch. It activates automatically whenever Find My is enabled and persists through remote erase. Once active, the device requires the linked Apple Account credentials to complete setup, erase, or reactivate. Apple removed its public Activation-Lock-by-IMEI checker years ago — there is no longer a reliable remote check by IMEI. The third-party "free iCloud check" sites pull from inconsistent caches; treat their answer as a hint, not proof.

The only real proof is on the device

Power on the device and watch the startup screen carefully — this is the single most important check on any iPhone.

• "Hello" / "Hola" screen visible: device has been properly erased. Proceed through setup and confirm no Apple ID prompt appears before reaching the home screen.
• Lock Screen or Home Screen visible: device has not been erased. Ask the seller to sign out of iCloud entirely (Settings > their name > Sign Out, with their Apple ID password) in front of you, then erase from Settings > General > Transfer or Reset iPhone.
• "iPhone Locked to Owner" screen (iOS 15 or later): Activation Lock is active. The seller must enter their Apple Account password or remove the device at iCloud.com/find. Without that, walk — or price as a parts-only outcome.

Remote pre-meeting screen (use with caution)

IMEI Pro (imeipro.info) offers a free Find My / iCloud status check by IMEI or serial. It returns whether Find My is currently ON or OFF. Useful for screening an online listing before a long drive, but not authoritative — the seller can toggle Find My off and remove the device from their Apple Account between your remote check and the meeting. Always reconfirm on the device itself.

The eBay listing intersection

eBay's Encouraging Illegal Activity policy explicitly prohibits the sale of "kill switch-activated electronic devices, including smartphones and tablets." An iCloud-locked iPhone is a kill-switch-activated device by Apple's definition. Listing one — even disclosed — risks listing removal and an account strike. Practical rule for the flipper: never buy a device with active Activation Lock unless the price reflects a parts-only outcome and you have a buyer for parts off-platform.

Parts and Service History — the "Unknown Part" line

Settings > General > About > Parts and Service History (iOS 15.2 and later). Each serviced component is labeled either "Genuine Apple Part" or "Unknown Part." An "Unknown Part" line affects three things at once: iOS will not display a battery health percentage for a nongenuine battery; the camera or Face ID may show reduced-functionality warnings; and buyers will screen for "all genuine parts" condition and open not-as-described claims if it was not disclosed.

AppleCare and warranty coverage

Enter the device serial at checkcoverage.apple.com — no login required. Remaining AppleCare+ coverage is real listing money: a recent iPhone with months of AppleCare+ remaining lets a buyer take a screen-damage repair to Apple at the AppleCare+ service fee instead of the out-of-warranty price, and that coverage carries to the buyer.

FRP is what bricks an Android after the wrong reset.

Google Factory Reset Protection (FRP) — called "Google Device Protection" in Samsung's documentation — is the Android equivalent of Activation Lock. It triggers when a device is reset via the Recovery menu (volume + power button combination, choosing Factory Reset from that menu) rather than through the standard Settings reset path. When triggered, the first boot demands the Google account credentials that were active on the device before the reset.

Why this catches buyers off guard

A seller can hand over a phone that was "factory reset" via Recovery mode. It looks clean. But on first boot, after connecting to Wi-Fi, the device demands the seller's Google account email and password before completing setup. If the seller is gone, the device is effectively a brick — bypass tools exist but are unreliable, often paid, and violate Google's terms.

Defuse FRP at the table — in this order

1. Settings > Accounts > Google > Remove account — confirm the Google account is removed.
2. On Samsung devices, also remove the Samsung account: Settings > Accounts > Samsung account > Remove. Samsung adds a second lock layer beyond Google FRP; the Samsung account will prompt for its own credentials if not removed first.
3. Settings > Lock screen > set lock to None — clears any pattern, PIN, or fingerprint requirement that could complicate setup.
4. Settings > General Management (Samsung) or Settings > System (Pixel/stock Android) > Reset > Factory Data Reset — performed from inside Settings, never from Recovery.
5. Boot through setup to a home screen without any Google or Samsung account prompt. Home screen reached = FRP clear. Any "Verify your Google account" or Samsung account prompt = FRP engaged and the device is locked to the previous owner.

Samsung-specific extras

• Knox warranty bit: dial *#1234# and read "KNOX Warranty Void." 0x0 is intact; 0x1 is permanently flipped — bootloader was unlocked or a custom ROM was installed, and Samsung Pay, Secure Folder, and corporate apps will no longer function. Disclose in the listing and price accordingly.
• Samsung diagnostic shortcut: dial *#0*# in the phone dialer to launch the built-in hardware test grid — R/G/B screen tests, touch grid, vibration, both cameras, sensors, speaker, receiver. One tap each. Replaces eight manual tests in roughly 90 seconds. Blocked on some legacy Verizon/Sprint Samsung devices; fall back to Samsung Members > Phone diagnostics.
• Samsung Members battery diagnostic: preinstalled on most Galaxy phones. Samsung Members > Support > Phone diagnostics > Battery test. Returns Normal, Weak, or Bad.

The full buy-or-walk sequence.

This is the on-device routine, in the order you run it. Total time per device is ten to fifteen minutes once practiced.

Step 1 — Pull and verify the IMEI before money moves

Dial *#06# and confirm the number matches the SIM-tray engraving and the original box if available. Run the IMEI through CTIA Stolen Phone Checker (stolenphonechecker.org) and Swappa's free IMEI check (swappa.com/imei). Both must return clean. Mismatched IMEIs across *#06# and the SIM-tray engraving mean a swapped logic board or counterfeit — walk.

Step 2 — Confirm all software locks are cleared in person

iPhone: power on the device and watch the startup. The device must reach the "Hello" screen after a full erase — not a passcode screen, not "iPhone Locked to Owner." If already set up, have the seller sign out of iCloud entirely (Settings > their name > Sign Out, with their Apple ID password) and then erase. Android: have the seller remove the Google account, remove the Samsung account on Samsung devices, set the lock to None, factory-reset from Settings (not Recovery), and boot through setup to a home screen with no prior-credential prompt. A locked device has zero resale value without the original credentials.

Step 3 — Read battery health and Parts and Service History

iPhone: Settings > Battery > Battery Health. Note the percentage. iPhone 15 and later also show cycle count and first-use date on the same screen. Then Settings > General > About > Parts and Service History — document any "Unknown Part" flag before agreeing on price. Android: Settings > About Phone > Battery, or Samsung Members > Phone diagnostics > Battery test. Pixel 8 and later expose battery health at Settings > Battery > Battery Health. For older Pixels and other Androids, AccuBattery (Play Store) gives a cycle-count estimate across one full charge cycle.

Step 4 — Run the full hardware sequence

Touchscreen swipe across every zone in Notes or a drawing app. Full-screen color test for dead pixels and burn-in (oledtest.org or deadpixeltest.net cycle solid R/G/B/W/black). All cameras — photo plus 4K video on every lens, front and rear, watching for haze, autofocus hunting, and purple tint. Microphone via Voice Memos (iPhone) or Voice Recorder (Android). Earpiece via a call to yourself. Loud speaker at full volume. Charging port with a known-good cable plus a wiggle test. Wi-Fi connect and speed test. Bluetooth pair with another device. Cellular with your own active SIM. Eject the SIM tray and shine a flashlight at the LDI strip — white or silver is dry, pink/red/purple is liquid exposure. On Samsung, also dial *#0*# for the built-in hardware test grid.

Step 5 — Make the buy/walk/parts-only call and document everything

Based on the results, the device falls into one of three categories: whole-unit flip (clean IMEI, all locks clear, battery at or above 80% or replacement cost priced in, all hardware passing, no liquid damage), parts-only buy (locked, bad ESN, red LDI, dead board, bent frame, Face ID irreparable — only if you have a parts-recovery pipeline), or walk (any check you cannot verify; sellers blocking IMEI checks, refusing factory resets, or pressuring "decide now"). For any device going to listing, photograph the IMEI display, the "Hello" boot or Android home screen, and the battery health screen on day of purchase — that file becomes your "received as clean" evidence in any future dispute. Re-run the CTIA blacklist check the morning you ship.

The full checklist on one page.

Print this, save it, or work from it on a phone next to the device. Every line is a single check with a single pass/fail signal.

Table 1 — The verification checklist

Table 2 — Red flags and what they mean

What the test results look like on the listing.

Diagnostic outcomes have to map cleanly to the condition tier you select on the eBay listing form. eBay's cell-phone category is more restrictive than most. The standard solo-seller conditions are New, Open Box, Used, and For parts or not working. The refurbished tiers — Excellent, Very Good, and Good refurbished — are gated and not available to most individual sellers.

How test results map to condition

• Clean blacklist + clean locks + all hardware passing + battery within resale range: list as Used. Photograph the IMEI display, the "Hello" boot or Android home screen, and the battery health screen on day of listing.
• Any failed hardware check that materially affects function (cracked screen with dead touch zones, dead camera, charging port that requires wiggle, OLED with visible burn-in, swollen battery, triggered LDI, IMEI mismatch, Face ID inoperative after a screen swap, FRP/Activation Lock locked): For parts or not working. A cracked screen is For parts or not working in eBay's cell-phone category, not Used.
• Any "Unknown Part" line in Parts and Service History: disclose in title or description, price to aftermarket comps, and consider listing as Used with explicit disclosure rather than a higher tier.

Best Offer and pricing format

Best Offer is not available in eBay's cell-phone category. Listings run as fixed-price Good 'Til Cancelled. Price accordingly — there is no negotiation lane, so the listed price has to do the work.

Frequently asked questions.

Next up: refurbishing and pre-list repair.

Now that you can tell a flip from a paperweight before money moves, the next spoke covers what to do with the devices that need work — which repairs pay back, which are traps, and how to keep "Unknown Part" off your listing.

Spoke 4: Refurbishing → ↑ Back to eBay Phone & Electronics Flipping Guide