Usually the factory warranty is voided if more than a certain amount of clear is gone. They will run a thickness gauge over it, and if it comes out too low, you're SOL. I can definetly see the market in an Autopian sense (I've wetsanded my own car to take out OP before), but I don't think the mass market is going to find the risk worth the reward (most people have no idea what OP is). Also, consider that you might make $2-300 per car, but one bad mistake is going to cost several times that. Unless you can get customers to sign a waiver, that's what I do whenever wetsanding is necessary.