Since buying second hand iPhone or in general second hand electronic devices is a serious issue, it would be advisable to follow the following guidelines:
1) Never deposit money in advance
2) Prefer a local seller from the same town or prefecture, in any case it is advisable to have a live meeting before the transaction.
3) Always know as much as possible for the potential seller ( name, mobile phone, land line etc) Be suspicious for any seller that provides only an email or only his mobile number!
4) Be very throrough with inspecting the iPhone in question. If you do not have the special knowledge refer to a specialist or a friend who knows better the subject. Physical inspection should be thorough including all major functions as well as power cord, headsets and any other peripherals. It would be advisable to have the seller fully charge the device and then inspect it only on battery power.
5) Be sure that the described device in the ad corresponds totaly to the real one.
6) Always proceed with the transaction in a closed space be aware of sellers wishing to continue with the transaction in an open space.
Most iPhone users are very proper in their dealings. However as all over the world there are in Greece too networks that are dealing with stolen, smuggled or second rated Apple devices. Be extremly vigilent in these cases and be aware when asked to pay in advance or be handed over faulty Apple devices.
Be vigilent!