I had an old iPhone where the previous owner had tried to repair it, but when reassembling left out a bracket that secured the camera connector to the motherboard. Dropping the phone would cause the connector to pop out, disabling the camera until I took the thing apart and reconnected it. Opening the camera app would just give a black screen.

At very least you're likely to get the error message about the serial number being wrong on newer phones, since the camera assemblies are serial locked.