Glad I took Auto's in HS, as the shop teacher said "if nothing else you will know enough to talk intelligently to the mechanics doing the repair". After HS I turned wrenches for a place that did farming, trucking and auto repair for customers. The diversity taught me alot. I can say we were a fair shop. Today I do most of my own maintenance and repair.
I have a story of my BIL took his Explorer to the Ford dealership in AZ. I think it was for tires. They said his AC was not working and quoted a cost for repair, he said don't worry about it. He had issues with a blend door or vacuum lines, so he figured he knew the problem. Come to find out they sabotaged something with the AC so it would not work, making something up when diagnosed it.
Also have my SIL that took her newer Chevrolet Eqinox in for a oil change. Apparently they over filled it and she drove across state. Not long into the drive it threw all kinds of dash lights. I never heard what the oil change did or paid the bill at the chevrolet dealer.
With just these examples I have very little faith in shops. I feel even the decent ones are trying to beat the flat rate pay in a damn big hurry.
I think back to yesteryear when you would take your farmall H-M in for service and there was a old IH mechanic that took pride in that winter overhaul.