Have you written any letters to the owner of the dealership? He may be unaware what practices his employees are following. If phone calls don't work, write a letter detailing the problem and requesting some action to resolve it. If you don't get a response, send a second letter with a copy of the first attached. Always keep a copy of your letters and always make the tone positive and friendly.
If all else fails, picket in front of the dealership, but make sure that anything you have on your sign is stating facts, not opinions, as you don't want to be sued for liable. A few hours a day standing out front may scare off enough potential customers to make them reconsider your plight.
