Repairs and Used Car Purchase

My sister was shopping for a used car that fit her price range. She found one and took it for a test drive. While on the drive, the car began shaking and the C.E.L. (Check Engine Light) came on. The mechanic on the drive said they would check everything on the vehicle, repair it, and then give it to her. The next day she went to pick it up, no light on, but drove a few miles away and the light came back, it began shaking again. The dealer was already closed, so she brought it Meineke who diagnosed many issues with the vehicle and said that the dealer only turned off the light. DO NOT SHOP THERE. They provide unsafe vehicles, they are a CHOP SHOP!