Tips on buying second phone:-
1) while purchasing any phone which is second hand always study careful of the phone.
2) purchasing second phone check it properly that it working properly, system not leging or hanging.
3) check the battery, of the use phone it working good or no. How old the battery is.
4) quality of the phone, body is good if the phone has any scratches then do check how the scratches is deep according to that only you purchase the phone or not.
5) while buying second hand phone never be in hurry take time check it very carefully at least you should check phone for half and hour. Then only purchase the second phone