The amount you'd save would be miniscule. The prep is the most important part, so why would you risk screwing it up for a few $ (Canadian $?). If the paint didn't stick, they could say it was your fault. My M-technic rear spoiler finally arrived for my car. It is currently painted black, and I will need to repaint it COSMOSBLAU-METALLIC. Is it cheaper if I sand it down myself before I give it to the paintshop? Or should I just pay more and let them do it. I also need to know how to seperate the rubber from the fibreglass part, so that the bodyshop doesn't have to do it.