It sounds like you are in a tough position because if you don't pay, the mechanic might sue you for services rendered even if unauthorized under a theory of quantum meruit (meaning you were unjustly enriched by the additional services). To beat that kind of claim, if the car is in no better state than when you dropped it off or is worse, which it sounds like it is, the best thing to do is get your car out of that garage immediately even if you have to tow it somewhere else and pay the mechanic for what you did ask for and which was properly performed. You could try bargaining with the mechanic to lower the price or search this website for attorneys who handle similar claims. You likewise may have a claim under the consumer protection act for the unlawful or deceptive acts or practices of the mechanic, and most attorneys are capable of handling those types of claims. You may also want to contact the Attorney General's office to file a complaint. This happens far too often and I would be surprised if you are unable to find an attorney to help you with this. Best of luck.
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This is a tough situation because a lot for a car repair isn't usually a lot for a lawyer to charge. I don't know of any lawyers who specialize in car repair overcharging.
Evaluating any legal question requires a detailed knowledge of the specific facts involved. Since a short question will rarely contain all the relevant facts, the answer here should be considered a general comment for your consideration and not legal advice.
You may be able to fight it. Start with the information below; see http://www.mass.gov/ocabr/consumer/autos/lemon-laws/mechanics-of-auto-repair.html
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