I try to avoid our local MB dealer exactly for this reason. Years ago, I had my front brakes done by the dealer. They replaced front rotors, pads and sensor. I picked up my car and about 3 miles later, I lost a front wheel, causing some damage to the inner fender. I had the car towed back to the dealer and found out that the wheel studs had been completely stripped, probably by the use of a too-strong air gun. "Not our fault" was their final answer.
I now do business with a very competent independant shop and I always watch what they do on my car.