if your worried about leaving your car at a mechanic, they stay with it while they work on it.
i once went to autoalley at paramatta with a mate, and there is a carwash accross from a caryard we were at. you just drop your car off and they wash it, then you pick it up later.
what the customers didnt know what they while the employees were washing their cars, they were also doing burnouts and thrashing them thru back streets.
this was in broad daylight, we were just sitting there watching them bag it up out the front of the car wash!
after that i vowed never leave my car at a mechanic in case they do it to my car, id rather sit there and wait.