When you fight it...try to get a written statement from the sales manager or the salesman stateing that this is the exhaust the car was sold with. That will help sway your way even more, even though its obvious the judge is going to say it's a waste of time. But just in case you get a dick and he says pay the fne, you can take the dealership to court and get your money that way...(or just talk to the dealership before taking them to court and make them pay, but be calm about it)
