Dnasty

My car has been squealing like a banshee for close to 2 months now... took it to the mechanic had him throw on rear rotors as there was a bit of a lip on it and that's what the mechanic said was the issue. I drove out the shop and notice the same squeal, prominent as ever... rolled my windows down and it appears to be coming from the front of the car. I took it back and had the guy look at it and hes basically telling me he has no idea what the issue is. Prior to this, the pads and front rotors were replaced around november of last year. There are burn in lines on the rotor that I am being told is due to many different reasons... living on a hill, making a few emergency stops, and the last which really seemed ridiculous was going to a car wash while the brakes were hot. I am also being told that this sort of issue is not covered under the brake/rotor warranty (these are supposedly genuine mercedes parts). Today I took it in and he said it needed a light resurface.. against my better judgement I let him do this and of course the noise is still there. Aside from coming back tomorrow with a baseball bat and demanding he give me new rotors and pads I'm not really sure what to do here. It's a guy who has serviced 3 other of my mercedes over 4 years and up until this happened seemed like a straight guy. Is there any truth to any of what this guy is saying? None of my other benzes had/have this issue had an s550 rotors and pads changed no squeal, had an e320 pads changed and squeal went away. Now his next idea is that I need softer brake pads even though he raves about using mercedes everything all day and night. Is 9 months a good amount of time before front brakes and rotors start to squeal?