MB mats have a foam backing and come with a metal clamp that secures the mats to the floor board carpeting. I guess the foam could rub off if the clamps are not used.
My 400E had aftermarket mats in it when I bought it. The aftermarket mats had a paper like, cloth like, sticky backing that was meant to hold the mats in place without clamps. I ditched them after about a week in the car because they were not "exactly" the right size and fit nor did the stickly backing keep the mats in place.