Mercedes dealers in particular are thieves. Mercedes-Benz of Boston tried to bait and switch me replacing an AC compressor on my 1999 E300D Turbo. Initial quote was $1750, after they had the car a couple days they made up some bullshit about the condenser being bad and said therefore it would be $5000. I told them to go fuck themselves, bought the necessary refrigerant handling equipment, and did it myself. This was 5 years ago. Still nothing wrong with the condenser.

IME it's 100% of the time better to buy whatever tools you need and do the necessary research to DIY than to take a car to a mechanic. And certainly never a dealership.

EDIT: Almost forgot. When I checked the pressure in the AC system after getting it home before working on it, it was super high. What I suspect they did (because I told them I wasn't going to pay their usurious rate) was just cram a bunch of refrigerant into the system from their recovery tank in the hopes it would blow seals and screw me over. So, yeah, avoid MB of Boston in particular.