Why does my camera look fine but not working?

My phone slipped outta my pocket and was ran over by a car. Screen shattered but back of phone was looked fine including the back camera. Was able to pay to repair the screen dude said home button and ear speaker for calling works fine also. The cameras both looked fine but when I opened the camera app it only shows a black screen, I also used apps that use the camera and also had the same issue. I tried many troubleshooting ways to fix the camera issue but nothing worked. The guy told me it could be an internal issue where the camera needs to be replaced or it is an issue with the camera and the motherboard. Could someone give me an answer?