No matter what the manufacturer says, all racks of this type will eventually mark and even dent your car's bodywork. You can stave it off by using extra padding on the points of contact, but in the end you will be left with marks.

I would check if some sort of hitch can be fitted to your car. The hitch on my car isn't actually rated for towing and limited to a 1.25" receiver, but enables it to carry a hitch-mounted rack. The rack and bikes never touch the bodywork of the car.