I am local, and was storing a Porsche for a friend.
While in storage, the clutch froze. The good news - they promptly towed it to the shop to do the work.
The bad news - they added 2 quarts of oil, which I knew it didn't need. (To check oil properly in a 911, the vehicle must be brought up to operating speed, which they admitted hadn't been done. Otherwise the oil sits low in the sump and can't be read properly.)
When I asked them to remove the extra 2 quarts of oil, I got attitude, and a long delay for an appointment. "Leave the vehicle for a day, etc. We'll do it when they get around to it."
Ultimately I had someone else do the work, and that mechanic got all my business for the next 20 years.
Silly business practice. Admit you made a mistake, bend over backwards to accommodate the customer, and it's a non-issue.