I have had two similar experiences. First, I recently had to have all of the 1/4 turn screws replaced on the Audi belly pan. Apparently too many uninformed mechanics had put too much muscle into trying to turn the "screws" and they were all sheared. (I discovered this when I heard the pan dragging down the street!) I had been taking the car to general oil change places.
Then, also on the Audi, I had the fuel injectors replaced under a recall/warranty claim. When I was checking the oil some weeks later I discovered that the decorative plastic cover on the engine hadn't been tightened; four 1/4 turn screws you could fasten with a dime. This time it was a dealer mechanic who rushed the job and made this oversight.
Conclusion? Overall no big deal, no major damage, and so I don't rant and rave. I am determined to find a good shop where they understand, and love, the German cars they work on, and then expect high quality work for fair charges.
Good things aren't cheap, and cheap things aren't good...
'96 E300D 56k mi
'95 Audi 90 118k mi
'92 GMC Suburban 138k mi
'85 300SD 228k mi