How to test a used phone before paying
The 5-minute inspection that catches 90% of problems. Run this checklist on every device before money changes hands. Skipping it is how new resellers lose $200 to a phone that turns out to be iCloud-locked.
The 12-point checklist
1. IMEI blacklist check
Dial *#06# to surface the IMEI on screen. Run it through the free IMEI blacklist check. Walk away on red — blacklisted phones cannot activate on US carriers and have effectively zero resale value.
2. Activation Lock / FRP off
iPhone: Settings → General → Transfer or Reset → Erase All Content. If it asks for the previous owner's Apple ID, the device is iCloud-locked. Don't pay until they sign out in front of you.
Android: Settings → Accounts. Confirm no Google account is signed in. If one is, the seller signs out in front of you.
3. Battery health
iPhone: Settings → Battery → Battery Health & Charging. Note the Maximum Capacity %. Below 85% reduces resale by ~$30; below 80% drops it a full grade tier.
Android: use AccuBattery, *#*#4636#*#*, or the OEM diagnostic. Same thresholds.
4. Screen — full-area touch test
Open Camera and Photos. Pinch-to-zoom across the entire screen, swipe through albums, tap each corner with a fingertip. Watch for dead pixels, color shifts, touch dead zones. Look at the screen at an angle — third-party replacement screens often show subtle color cast that disappears head-on.
5. Cameras (all lenses)
Take a photo with each rear lens (wide, ultrawide, telephoto if equipped). Switch to video, do a slow pan. Look for focus hunting, blurriness, "Camera Not Available" errors. Front camera: take a selfie. Test flashlight while you're there.
6. Face ID / fingerprint
iPhone: Settings → Face ID & Passcode → Reset Face ID, then re-enroll. If "Move iPhone Lower / Higher" loops, the TrueDepth module needs replacement.
Android: Settings → Security → Fingerprint → re-enroll a fingerprint, then test it five times. Capacitive sensors are usually reliable; ultrasonic (Galaxy S series) degrades silently.
7. Speakers and microphone
Play a video at full volume — both speakers should produce sound on stereo-speaker phones. Record a 5-second video and play it back to test the mic. Test the earpiece by making a brief call.
8. Charging port
Plug in a charging cable. Should show charging indicator immediately. Wiggle the cable gently — should stay connected. Try a USB-C-to-USB-C cable to test data transfer if you have a laptop handy. iPhone 15+ and most modern Androids: confirm the port works in both directions (charging in, output out).
9. Wi-Fi and Bluetooth
Settings → Wi-Fi → connect to your shop's Wi-Fi. Open a website. Settings → Bluetooth → confirm it scans. Both should work; failures here are uncommon but expensive (logic-board level).
10. Cellular signal
If the phone has a SIM, check signal bars and try a brief call or data session. If unlocked + no SIM, the seller can't easily prove cellular works — note that as risk in your buy price.
11. Carrier lock status
iPhone: Settings → General → About → Carrier Lock. Should read "No SIM restrictions" if unlocked.
Android: pull the SIM tray, check "Network" or "SIM status" in Settings. On Galaxy, the device's IMEI status page shows lock state.
12. SIM-tray IMEI match
Pull the SIM tray. The IMEI printed there should match what *#06# displayed and what's printed on the box if available. Mismatch means the device has had its logic board swapped — these are rebuilds with unpredictable warranty status. Walk away.
The 5-minute target
Practiced, you can run all 12 checks in under 5 minutes. New resellers should plan 10–15 minutes per device until the muscle memory is there. The cost of skipping is high enough that it's never worth rushing — a single skipped step can erase a week's margin.
What to do if a check fails
- Hard fail (IMEI blacklist, Activation Lock): walk away. Don't negotiate down.
- Functional fail (camera, sensor, screen issue): negotiate to repair-cost-aware buy price, or pass.
- Cosmetic fail (worse than claimed grade): negotiate down by one grade tier's price.