Reminds me of a very similar circumstance.
Because I used to turn a wrench or two I decided to pop the Derby and check the adjustment myself. Found the 11/16" nut backed off and not at repair mamual specs. Another time after having a Big Bore Kit installed the Throttle cable had about 1/2" play. When advising the dealer they reply "why didn't you bring it back?".
I work in the auto industry and the same thing happens there. Everyone is on "the clock" and the pressure is on to produce. One little interruption and momentum/memory is lost etc etc.
That's why when you find the right shop,pray that they can stay in business taking the time to do quality work. I personally will buy my "stuff" there and probably pay a little premium due to their smaller size but I want them to succeed.