Got my ML back from service A today and on the paperwork it said something about my brakepads and "customer declining service" (which I never got a call about). It stated my fronts were at 10MM and the rears were at 9MM. Just wanted to know if this is normal or not and how thick (or thin) they need to be before replacing them. TIA.

10mm has heaps left, usually you think about replacing (as a service tech) at about 5mm, the wear sensor comes on at about 3mm. You have brake wear sensors, don't worry about it.

Thanks!

I am curious what others are being quoted for replacing the brakes? My Stealership says my rears are going to need replacing and quoted me around $1000. They said that the never just replace the shoes rather opt for rotors/brakes and some other things outlined by MB policy. Is there a reason that AMG/MB needs new rotors every time the shoes are worn?

Mine were at 9mm on the rear.

You don't need rotors with every brake pad change. Rotor wear varies with the driving style so there is no definitive number of pads between rotor changes.

You only need to replace rotors when they are close to the minimum thickness or are damaged nessesitating replacement (eg. cracked).
Some dealers like replacing them all the time, just ask what the minimum thickness is and what your rotors measure.