My guess is that it's not a Mercedes dealer that is selling this and that is a reason why there's no Starmark on it.

I wouldn't worry about the curb rash on the rims, since they are 17's with low profile tires the rim sticks out further than the tire so it hits the curb first. So just the slightest touch on the curb gives bad results on the rim. You should see all the MB, BMW, and Porsche rims out here in LA.

The bumper is probally caused by the previous owner hiting a curb when parking. The owner pulled up to the curb 'til the tire hit the curb hitting the bumper and dragging it everytime he/she parked.

The car still should have the remainder of the factory warranty left on it so I wouldn't worry about it. Bring it to a MB dealer and have it inspected just to see if there is any damage that isn't noticable. My guess is that you could easily get the price down more if you make a big deal about the bumper and the rims. I can't imagine it having any major damage, mechanically.

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1992 Mercedes-Benz 400E
2002 Mercedes-Benz ML500