I would ask them to put in writing why they recommended the work they did. Then you have something to compare to the actual recommended maintenance requirements. With that you have something to show to BBB. First, I would talk to a manager and try to get a significant discount. If they do right by you, you're good. Otherwise, you take it further. This is something that you could also take to small claims court and if you have something in writing, it should be an open and shut case.