I've had too many situations where the shop has actually screwed something up. A Jiffy Lube place stripped my pan threads and I didn't find out until the next oil change at Walmart. Had to helicoil it which luckily held until the vehicle died of other causes. Of course, the Jiffy Lube place denied it. Same vehicle, I had my wife take it in to get the brakes done because I was busy with work (never let your wife take a vehicle in for repairs ). They totally jacked her around and charged an absolutely ridiculous price for what amounted to changing the pads on the front rotors. I don't normally scream and yell in public but I was livid with these people. I pulled the wheels and brought the rotor & caliper down to the shop. Both were replaced on the invoice but were clearly original parts. I got my money back but it was totally not worth the drama.
On the same vehicle, I had a tuneup and the vehicle checked before a cross-country trip. They stripped the head putting in a spark plug and of course said nothing... letting me deal with it after I was 2000 miles across the country.
I have still taken my vehicles to shops but I watch them like a hawk now. If they won't allow me to watch while they work I go elsewhere. Luckily now I have a guy that is pretty good whom I trust. I do all my own basics, brakes, filters and such but I've had jobs I just didn't want to do (plugs on full-sized van) that I've taken over to him and he squares me away. A mechanic that you trust is hard to find so when you get one take good care of them.