One quick change company insisted that my 74 Olds Custom Cruiser differential needed oil added and also changed. They also said it needed a new air filter and PCV valve. Since I had just changed these the week before I didn't believe them. I checked the differential and it was obvious they had not even removed the plug to check it.
Last year another quick change company overfilled the same car with oil. (I;m not a slow learner but I was thousands of miles away from home and needed an oil change). While I waited from them to drain the overfilled oil I met a furious customer who'd been waiting for 3 hours for them to find a new transmission filter for his Ford pickup because they had mistakenly drained the transmission instead of the engine!