Settings → Battery → Battery Health. Cycle count: Settings → General → About (iPhone 15 and newer).
Below 80% means a replacement is due.
Under 300 is great; over 800 is heavy use.
Snap the front, back, edges and the Battery Health screen.
iCloud / Find My signed outMust
Settings → [name] must be empty. Locked phones are useless.
IMEI clean (not blacklisted)Must
Dial *#06# and check it on an IMEI checker.
Face ID / Touch ID worksMust
Set up a test face in Settings → Face ID.
SIM / network works
Insert your SIM, make a call, check signal bars.
Display: no dead pixels, burn-in, tint
Open a full white and full black image.
True Tone available
Missing in Control Center = screen was replaced.
All cameras + flash work
Test every lens, zoom, video, front camera.
Speakers + microphones
Record a voice memo and play it back.
Buttons + silent switch
Volume, power, Action button / mute switch.
Charging port + wireless
Plug in a cable; try MagSafe if available.
Wi‑Fi + Bluetooth
Connect to shop Wi‑Fi and a Bluetooth device.
Body straight, no dents / swelling
Lay flat on a table; check screen lift.
Settings → General → About → Parts and Service History. 'Unknown part' means replaced.
Battery
Display
Camera
Dial *#06#
About → Model Number, e.g. LL/A = USA