Ever wonder where most new car dealerships make most of their money? Not selling cars, but repairing them. Yep, the service department is the key place where the money is made by upselling repair and maintenance work; but sometimes, that work isn't needed or required for your vehicle. How do you know which repairs are legitimate and which ones are a fool's errand? Well, we gathered up and picked the four common upsells and repairs that you can definitely pass on.