Don't really need laws -- years ago I took my CRX in for work at a dealer I trusted. When I came to pick up my car, there was Taco Bell garbage on the floor. I confronted the manager about it, and at first he denied it, but the evidence was overwhelming, so he apologized. I told him to save it, as that was the last business he'd ever get from me.
A couple years later, they were out of business. I wept not.
No more laws, please -- our society has already drifted too close to authoritarianism for me. If something of significance does happen to your car, there are always civil remedies.
The legal system is not a remedy unless it's a small amount of $$ you can pursue in a small claims court. This sort of practice should have some strict consequences attached to it other than 'sue me' which is far too expensive to do unless you have the $$$ and the stake is large.
I don't want to have to worry that someone is going to take my car for a joyride because there are essentially no consequences. Look at the people who have had their cars wrecked from joyriding dealership employees or valets, in most cases they end up screwed because dealerships don't want to do the right thing.