Had a good experience with them when I had a starter issue with my car. Then had an issue with a fuel injector failing. They quoted $1100 to fix the issue and, at the time, made sense as the manifold had to be pulled off the engine. That was outside my budget so I checked with 3 independent mechanics. All of them were amazed by the quote and each said the labor itself would be no more than $200. Finally found a good mechanic and he fixed it in about 2 1/2 hours for $260 total including parts. I can see some disparity between prices but the $1100 was obviously a huge gouge.
My car is a bit old so maybe they just did not want to work on it. In any case, I will be using my independent guy from now on and not Marshall's.