Are you able to test it or are you buying it online? I'd be wary of anything online unless it's a trusted seller with a well-defined return policy. If you are able to test it first hand, then try the camera, WiFi, and Bluetooth to start. If any of those don't work or are wonky, then move on. While it may be something fixed by a hard reset, which you'll want to do whether there are any noticeable problems, I'd steer clear if there are any possible hardware issues. Assuming that stuff checks out, ask about the battery and whether it's the original. If yes, then you'll want to buy a replacement and depending on the price for it plus the phone, you may be able to find a new phone on ebay. Not sure where you're located but I just checked and there are a few for $200 USD or less.