If you really want to get tweaked, read the service manual and see what you got for your $300. I never have found a Mercedes dealer that didn't charge up the ass for everything... I don't think it's necessarily because they are crooks but because they have a flat rate manual that allows a generous amount of time for something that can be done quite quickly by a skilled technician.

For example, suppose there was a manual for cleaning the kitchen and for each dish you needed to load into the dishwasher, they allowed 3 minutes to account for opening the dishwasher, pulling out the rack.. placing the dish in the dishwasher... replacing the rack, adding soap, closing the door, starting it and then cleaning up afterward. Given that "flat rate" you would be allowed about an hour to load your dishwasher... something that can probably be done in 10 minutes or less.

Then there's the biggest rip off of all.. "shop materials". That's simply extra profit they explain by saying it covers the various things like a rag they might use to clean their hands.. or a squirt of WD40 on a noisy hinge. Find a local independent mechanic you can trust and take your car to him.