What to check when buying second 2nd hand or used iPhone

Check these things
1. Body, check for dents or scratches
2. Screen sensitivity - Try the screen by opening applications or typing letters to know wether it is still sensitive...
3. Ask for 1 week warranty to check the battery life. Normally for used iPhone, the battery life is 12 hours when used and 24 hours less used or standby.
4. Check wi-fi. Go to setting-wifi. Look for wifi and test it. This is important as repairing wifi chip is expensive.
5. Check signal. Insert your own SIMcard to check if there is signal.
There are two kinds of iPhone: Factory unlocked (no carrier attached-free to use with any SIMcard) and Software unlock (with carrier attached-need to be unlocked if you wabt to use with any SIMcard), so make sure your iPhone is unlocked.
6. Check sound. Play one song or ringtone to check it.
7. Check headset jack. Insert the headset jack, it should appear headset on the screen.
Remove the jack- push the volume button up and down- it should appear ringer on the screen.
Please be sure of these:
Jack in : headset appear on the screen
Jack out: Ringer appear on the sreen
Because it can be other ways, means the jack is damaged