Always buy second hand phone from the person whom u knw personally. or is from a reputed site or company. check the mic. call quality. sim slot. headphone jack. usb jack. after this go to settings. about phone. and check serial no. match the serial no. with one u will get on web. . always buy phones with proper. bill box. check imei no. on phone and box. to check imei. dial * #06#.i personally recommend u to buy second hand phones. but with proper care.be aware of. fake products. on buying an iPhone u are more likely to get. fake one. check with care the serial no. on back of phone and compare it. by finding. no. on Google