Most of us do our maintenance ourselves. In fact, many (most?) of us do our own troubleshooting and repairs as well.
Other than that, you've got to find a place familiar with Mercedes products. I stumbled onto a four - brother shop that did not indicate such experience, but when I stopped by to ask about getting brakes done, one of the four guys started telling me, "YOu know, that's really a Mercedes SLK320 you have there..." (His wife drove a VERY high miles '320.)

I knew right then I had the right shop..... but that was back in GA. I have no such resource here in Arkansas - I take care of my car myself and when I needed a fuel pump, I drove up to Olathe, KS and a forum member put it on for me.