If you are looking for a second hand mobile phone.its good idea because it is saving of money and if you want buy a new in future then also no problem.when you buy a second hand phone the main first thing you shoud see is that the phone is repaired or not.
Because if a phone is repaired then there is chances to be again fault in phone. So do not go for these phones even if there is low price they are in high risk.and then see the condition and use it for a day and buy in reasonable price.