What is the biggest scam an auto mechanic ever tried on you?

This is a whopper…. The authorized agent of MB tried to bill me $18,500 for a new engine block that they themselves damaged. I refused to take possession of the car and contacted MB in Germany, they sent an engineer to inspect the car and determined that indeed the block was damaged during an earlier service (the agent had overtightened a head bolt causing it to snap then drilled a new hole in the head and block which penetrated the water jacket). MB gave me a complete new engine and had it fitted by a different agent.