Check for Signs of Damage

This step is pretty obvious when it comes to looking for dents, scratches, cracks, and blocked ports. However, we want to call out one sign in particular that many buyers aren’t aware of: The moisture sensor. Look carefully by the charging and headphone ports on your iPhone, or in the SIM tray. If you see a tiny red dot here, that means the moisture sensor has been activated, and that iPhone was probably dropped in water. You don’t want this model, because it’s very hard to know how much damage the water has caused.