Hello, I recently got my first iPhone from someone off Craigslist. After I purchased it I noticed that the touch ID sensor did not work. I got online and saw that some people had issues after the last update to their phone so I thought nothing of it. Yesterday when trying to upgrade to iOS 9 I got an error 53 and was unable to update or back up my phone. I looked into the error and many reported it was an issue with a screen replacement and the Touch ID sensor and there is no way to fix it. I have contacted Apple and they are going to replace the phone after they check to make sure nothing was done to the hardware. What all do they check for when they do this? I am unsure if a screen has been replaced, but is that even something that would check for when checking for a hardware failure? Thanks!