Make sure you read all of the contracts that you sign and especially the inspection sheet. Your driver will do his best to get your car back to you in the exact condition that it was picked up in but generally things like leaking fluids, mechanical and electrical systems, loose parts, and weather will not be covered. These are things that are completely out of the control of the driver. If there is a very obvious part that is loose on a car then the driver will definitely remove it but he can’t be blamed for an engine failure when the only time that he moved the car was up and down the trailer.
So what is covered? Any driver negligence. Any scratches caused by loading or unloading or really any damage done while the car is in the driver’s hands outside of the things I mentioned earlier. But remember that all companies have different policies so read before you sign!