With an open carry transport, vehicles are subjected to outside elements. With longer distance transports, cars can get a little dirty or dusty upon arrival. A car wash will remove this.
It is extremely rare that any cosmetic damage will occur during the transport. As elements on the road will come forward and not to the side, they will normally hit the trailer cab first. All drivers are required to have up to 100,000 dollars in insurance in order to carry multiple vehicles.