Sometimes it's best to go to the dealership. Just because. I always ask to see my oil filter during an oil change.

Two things to look for in Mechanics:

First: ASE certification. This is the Automotive Service Excellence rating. In fairness, it's like a black belt in Karate. Sounds impressive, many are awed by it, but it really just means you know ALL of the basics. These are mechanics who KNOW cars and how to fix them. So, it's nothing to sneer at. I am just emphasizing that it's just the basics.

Next is ASA: Automotive Service Association. This one is key as it is effectively a union of Mechanics who have taken an oath to do right by their customers. When I break down in the middle of no where, and I know nothing about any Mechanics in the area, I look for an ASE/ASA sticker in the window, or these days search on the phone/web for same, that are local. I have had at least one breakdown where I was rather worried that the car was going to be a very expensive fix, only to have an ASA guy say "nah, just needed a $1.50 part and 10 minutes of TLC" and off I went... and my car condinued to work fine the rest of my trip and until I got home.

Once you find an ASA/ASE mechanic, treat him/her like gold as they are exactly that. Take a prospective used car you want to buy to them and ask them to give the car an inspection BEFORE buying it, etc.

Another trick is to go to your insurance agent. Ask them who they'd suggest to take your car to for repairs. They have to deal with this on occasion. Sure, it's body shops you'd expect them to know most about but every accident also has other function problems likely, thus they need to know about just mechanics too.

But, I agree, your schmoe sounds like a schmuck. Spread the word, far and wide. Let him suffer for the reputation he has earned. Oh, first, go to the Better Business Beureau and lodge a complaint. See if the guy who bought your moms car will write up a report about the experience so that you have multiple points of view to work with (this way it doesn't come across as "she said, he said" ).

Well there is always drawing a chalk line behind the back tire when you drop it off to make sure they actually moved it?

Also using a grease pencil on things that are to be changed out - to make sure it happened.

My niece just went through a spark plug drama. (Had to borrow my sisters car for weeks - thought for sure it was the tranny).
Apparently with the new computer system they checked Every Single Other thing and finally went through like an old school mechanic would and found - you guessed it! A rotten spark plug.

It was described as "Furry". If you've ever seen a battery terminal that needs cleaning you get it.

And yes there are some places that are terrible. I knew just enough when I still had a car to keep mechanics from trying that crap with me. Now? I can only imagine.