Not really his fault if people cut infront of him. I have had people cut infront of me on the way back to the lodge and have had to carve hard just to evade them. Greenies are assholes when it comes to skiing etiquette.
The magic eraser is probably your best chance, maybe if that doesn't work you could try "Bike grade" foaming simple green.
What kind of marks are these, scratches, scuffs, grease?