After buying iphones for family and mates for a few years, I have often come across some phones in mint condition, and some right lemons. As such, ive compiled a list of a few things to keep an eye out for when you go to buy an iPhone second hand, in particular for when you are buying an iphone off a dodgy lad in trekkies in an even dodgier neighborhood.
Things to ask the seller before meeting:
1. Whats the IMEI number? After you get this, ring up your phone network, tell them you are buying an iphone and want to check if the phone is stolen/replaced on insurance (i.e blocked). They will request this number off you.
2. What is the iPhones serial number? You can use this on the apple website https://selfsolve.apple.com/agreementWarrantyDynamic.do to see when the phone was bought (useful to collaborate the sellers story with), and if the iPhone is still in warranty (handy if there is something wrong with the iphone that you want to get repaired yourself for free by sending it back to Apple). Also, if the phone is over 12 months old and locked to a network, the network is required to unlock it for free.
Tools you will need to bring with you when meeting the seller:
1. A sim card on a network that the phone will accept (if the phone is unlocked, you can bring any network sim card).
2. A sim card removal tool, such as a paperclip or a thumbtack.
3. Optional: A small torch
4. Optional: A second iphone, to enable a "wifi hotspot" with.
5. Optional: A set of headphones
How to check if the iphone is functioning fine (these are in descending order of importance):
1. Put in a sim card (make sure its a micro sim card for the iPhone 4) ring someone, and ask them to ring you back. This tests the ringer, speaker, microphone, network signal, and most importantly, if the phone isnt blocked.
2. Hold your finger down on an icon to move it, and move it all around the screen. If it springs away from you at the same point repeatedly, then the digitizer may be damaged.
3. Take a picture. This checks the camera.
4. Turn silent switch to speaker and then switch it back to vibrate. If the phone doesn't vibrate, then either the vibrator is bad or the switch is bad.
5. If available, check to see if wifi is working by making a search for networks nearby. If you have a second iphone, you could enable "hotspot" and see if you can find that.
6. Press the on/off button to see if it wakes and goes into sleep to ensure that the button is working correctly.
7. Press home button to go to SpringBoard (the normal background) a few times to ensure its working correctly and isn't stuck.
8. Check the water damage indicators with a small torch: http://support.apple.com/kb/ht3302
9. Plug in headphones, and ring someone, and have a quick conversation. This checks the headphone jack.
10. Change the volume up and down. Check if the volume icon changes accordingly on the screen. This checks the volume buttons.
11. Remove any screen protector or case. Look at the cosmetic condition. Look for scratches on screen, back, scuffing on the trim, cracks near earphone jack and charger.
If im missing anything, give us a shout, I will add them to the list. There is more information available here: