We buy and sell used phones every day. This is roughly the order we check them in, and you can do all of it standing in front of the seller.
1. The IMEI, first and always
Dial *#06# and compare the number on screen with the one printed on the box and in Settings. If they do not match, walk away. Then text that IMEI to 8484 to see its PTA status before any money changes hands.
2. Activation Lock
This is the one that turns a phone into a brick. Open Settings > [owner name] > Find My and make sure Find My iPhone is switched off, or ask the seller to erase the phone completely in front of you and set it up fresh. If it asks for someone else's Apple ID during setup, the phone is locked to them and nobody can undo that for you.
3. Battery health
Go to Settings > Battery > Battery Health & Charging. Anything above 85% is healthy for a used phone. Below 80% and you should be budgeting for a battery replacement, so factor that into the price.
4. Parts and service history
On recent models, Settings > General > About lists parts that have been replaced. A note saying a part is unknown or not genuine tells you the phone has been opened, which affects both reliability and resale.
5. The physical checks
- Face ID or Touch ID: enrol your own face or finger. If it fails, the sensor is damaged and it is not cheaply fixed.
- All cameras: front, main, ultra-wide and telephoto. Switch between them and record a short video.
- Screen: show a white image and a black image full screen. Look for dead pixels, lines and discolouration at the edges.
- Speakers and microphone: play music, then record a voice memo and play it back.
- Charging and ports: plug it in and confirm it charges. Try a pair of wired or wireless headphones.
- Buttons: volume, power, and the action or mute switch.
- Water damage: look into the SIM tray slot with a torch for a red indicator.
6. The paperwork
Box, original cable, and a receipt if there is one. None of these are essential, but together they are a decent signal that the phone has had one careful owner rather than four.
A note on price
If the price is far below everyone else's for that model and condition, there is a reason. Usually it is the PTA status, the battery, or a replaced screen. Ask directly; a straight seller will tell you.
If you would rather skip all of this, every used phone we sell has been through these checks already, and you are welcome to repeat them in the shop before you pay.