I had a similar experience, but I never needed to go back to the shop after my one shady interaction. I just wrote and signed a letter of complaint, as well as provided some paperwork that supported my story. They were able to discover other cases of foul play after I pointed them in the shop's direction. It was one specific employee rather than the owners/management in my case. I'm sure he got fired and I'm not sorry. I hope I never have a similar experience again though. Even after I knew that guy didn't work there anymore, I never went back.