This is a working checklist, not an essay. Print it, screenshot it, or pull it up on your current phone while the seller waits. Twenty checks, about fifteen minutes, in three passes: exterior (5), function (10), software (5). If you want the why behind each item — what certification means, how shop and private-party risk compare — that's covered in our certified used iPhone buying guide. This page is the how.
Bring three things: a paper clip or SIM tool, your own charging cable, and your own SIM (or an eSIM-capable carrier app) to test cellular.
Three items on this list are marked [DEALBREAKER]. If any of them fails, do not negotiate — walk away. Everything else is a price conversation.
Pass 1: Exterior — 5 Checks (3 minutes)
☐ 1. Frame and corners. Run a fingernail around the aluminum or titanium rail. Deep dents at corners mean a hard drop — and hard drops are how board-level faults begin. Set the phone flat on a table and check it doesn't rock: a bent frame is a structural write-off, not a cosmetic one.
☐ 2. Front and back glass under angled light. Tilt the phone under a light source. Hairline cracks hide in reflections, especially at the edges and around the camera plateau. Back-glass cracks matter more than sellers admit — they're a real repair cost, not just cosmetics.
☐ 3. Camera lenses. Look straight into each lens with your flashlight on it. Scratches on the lens glass show up in every photo the phone will ever take; fog or dust inside the lens means moisture got in.
☐ 4. SIM tray and liquid indicator. Eject the tray with your SIM tool and shine a light into the slot. The liquid contact indicator should be white or silver. Red or pink = the phone has been wet [DEALBREAKER] — water damage is progressive, and today's working phone can be next month's dead one.
☐ 5. Screws and seams. Check the two pentalobe screws beside the charging port: chewed heads mean amateur opening. Check the screen sits flush with no gap or lifted corner — a proud screen edge means a bad reseal or a swelling battery.
Pass 2: Function — 10 Checks (7 minutes)
☐ 6. Display panel. Open a pure black image fullscreen: OLED black should be ink-dark and even, with no bright spots, lines, or burned-in ghosts. Then a pure white image: check for tint patches and dead pixels.
☐ 7. Touch, every zone. Long-press an app icon and drag it slowly through all four corners and the center. If it drops mid-drag, that region of the digitizer is dead — a classic symptom of a cheap replacement screen.
☐ 8. Face ID — enroll, don't ask. Settings → Face ID & Passcode → set it up with your own face, then lock and unlock. Face ID is the most common casualty of sloppy screen repairs and one of the most expensive things to be surprised by. A seller who refuses this test has answered your question.
☐ 9. Both cameras, all modes. Photo, video, flip to selfie, portrait mode, flashlight on/off. Watch for focus hunting, black screens on one lens, or a rattling/buzzing noise — failed optical stabilization rattles when you shake the phone gently.
☐ 10. Speakers and microphones. Play music (top and bottom speakers both fire), then record a voice memo and play it back — that one test covers the mics. Crackle or muffle means speaker or liquid trouble.
☐ 11. Every button and the mute switch/Action button. Volume up/down, power, mute. Mushy or stuck buttons are annoying; a non-clicking power button on a water-exposed phone is a warning.
☐ 12. Vibration. Toggle the mute switch and feel the haptic. A weak, buzzy, or silent Taptic Engine is a real repair.
☐ 13. Charging — your cable. Plug in your own cable and confirm the charge icon within seconds. Wiggle gently: intermittent contact means a worn port. If the phone supports MagSafe/wireless, rest it on a pad if one's available.
☐ 14. Wi-Fi and Bluetooth. Join a network, load a page. Toggle Bluetooth and confirm it scans. Grayed-out Wi-Fi or Bluetooth settings are a board-level fault — priced accordingly, which is to say: walk.
☐ 15. Cellular with your SIM. Drop your SIM in (or activate eSIM). Confirm signal bars, place a real call, use mobile data. This simultaneously tests the antenna and smokes out carrier-locked phones sold as unlocked.
Pass 3: Software — 5 Checks (5 minutes)
These five find the problems that polish can't hide — and three of them are dealbreakers.
☐ 16. IMEI blacklist check [DEALBREAKER]. Dial *#06#, note the IMEI, and run it through a blacklist checker on your own phone before money moves. A blacklisted iPhone — reported lost, stolen, or attached to unpaid financing — cannot be activated on US carriers. No discount fixes it.
☐ 17. Activation Lock — watch the sign-out [DEALBREAKER]. Settings → [name] → Sign Out, with the seller entering their password, then Erase All Content and Settings, in front of you. When the phone reboots to "Hello," pass the setup until you confirm no Activation Lock screen appears. An iPhone tied to someone else's Apple ID is a paperweight, whatever story comes with it.
☐ 18. Parts and Service History. Settings → General → About → Parts and Service History. "Unknown Part" beside Display, Battery, or Camera means non-genuine or unverified components — read the details in our certified buying guide. Not automatically a walk-away, but it caps what you should pay.
☐ 19. Battery health. Settings → Battery → Battery Health & Charging. 85%+ is a comfortable buy; 80–84% means subtract a battery replacement from your offer; below 80% or a "service" flag, the price must assume a new battery. Replacement is a routine repair — make it the seller's discount, not your surprise.
☐ 20. Carrier lock and spec match. Settings → General → About: "Carrier Lock — No SIM Restrictions" for an unlocked phone, and confirm the model and storage match what was advertised. A "256GB" listing that's actually 128GB is a $50+ lie you catch in ten seconds.
Scoring It
- Any dealbreaker fails (4, 16, 17): walk away. No price is right.
- Items 18–19 imperfect: buy only with the repair cost subtracted — that's your negotiation script, with real numbers from our repair price guides.
- Everything passes: you've done a better inspection than most shops that stamp "tested" on a listing.
And if this list feels like a part-time job — that's the honest pitch for certified. Every device in our pre-owned inventory has already been through this entire checklist by the same technicians who repair iPhones all day, and it's backed by a 90-day warranty at all nine stores, including Rowland Heights and Alhambra.
Frequently Asked Questions
How long does the full checklist take? About 15 minutes once you've done it twice. A meaningful seller will wait; a seller who rushes you is telling you which items would have failed.
What if I can't test cellular because I don't want to remove my SIM? At minimum, confirm Carrier Lock says "No SIM Restrictions" (item 20) and the IMEI is clean (item 16). But a two-minute SIM swap is the only true test of both the antenna and the unlock claim.
Can iFixForU inspect a phone I'm about to buy from someone else? Yes — bring it in during the meetup. Our free diagnostic covers the functional checks with shop tools, and any of our locations can run it while you wait. Book a time so a tech is ready.
Is a phone with "Unknown Part" on the display always bad? No — quality aftermarket screens exist. But it proves an undisclosed repair happened, so the listing's honesty is now in question, and the price should drop to reflect an unverified panel.
The Short Version
Exterior tells you how the phone was treated, function tells you what works today, software tells you whether it can legally and practically be yours. Run all three passes, respect the three dealbreakers, and negotiate the rest with repair prices in hand — or skip the homework entirely with a certified device that arrives with this checklist already signed off.
