I have no problems with brake squeal on the brake jobs i do, and my service advisor will often give me other techs come-backs for squeal. It's important to wire brush the areas that the brake pad backing plate contacts, also the back side of the pads that the piston or caliper contacts. Then these areas should have a brake pad lubricant applied, I don't recommend the rubbery stuff, use a grease that is designed for this purpose. MB was having a hard time with squeal on some of the ML's, on the V8's particularly, they have a different caliper than the V6. They came out with a recommendation for a different type of brake pad grease for these trucks called Moly-Kote, there is an MB part number for ordering Moly-Kote, but the dealer should have a tube of it. The point being that this is the grease I have been using lately, so maybe the dealer can try using this stuff, instead of what they used previously, which I assume may be "nothing". I won't be able to post the part number for Moly-Kote for over a week, I'll be in MB training for brakes--Oh no wait, transmissions!
On MB pads, there is already a thin aluminum plate on the back that also should help with quieting the pad noise.
I agree with the previous post in regards to "bedding in" the new pads, but it's a cop-out to expect the owner to somehow do this themselves. The best bed-in procedure is to simply take the car out and do a series of hard stops, the brakes should "feel right" when you are done doing. Shouldn't take much more than a mile to do this. Don't brake so hard or so often that the brakes are overheated or fading. Brake just before the point that the ABS activates. At first you won't be able to hardly get to that point, but after a couple stops, you have to be careful to not reach the ABS intervention point, as the brakes will be quite effective.