Six months ago I paid for a part to be replaced, paid for it, and while scrapping the car for parts today discovered they never replaced the part.
This was discovered because my step-father had written in permanent marker on the old part which is normally hidden by the engine. This particular part caused the check-engine light to come on for what seemed to be a false-positive. It would claim there was a problem with the transmission even though I had just replaced that part. Well the car finally broke down completely while in use. Luckily I was not injured. But it was finally time to scrap the car. While taking it apart, surprise surprise, it was discovered my step-father's writing was still on the part they said they replaced. I paid for the new part. I paid for the labor. It doesn't look like they did any of that. As far as I can tell, they took the money and then used their engine checking tool to just clear the check-engine light warning so that it would not come up until after I drove off the lot.
In short, they are crooks. They ripped me off because they thought they could get away with it (and they did get away with it). I'm sure they will rip you off to if they see the chance. If you are on the road when your car fails, I pray you do not die due to their greed.