Can apple tell if I dropped my phone

Hey i got this phone as a gift from my best friend as she upgraded to the iPhone 7+ and did not need this phone anyway prior to her giving me this phone she threw it and it hit a wall the phone looks perfectly fine but the rear camera does not work and I've finally decided to do something about it the phone is still under warranty so Apple gave me an appointment to meet with a genius to get this replaced and they said that they will see if this is my error or theirs and will replace it no problem if it is there problem my question is how can they tell if it's my or their problem