Your buddy has to go and take out a mechanic's lein. After a set period of time has lapsed, if the work hasn't been paid for, then he can either put it up for auction, for sale, or keep it for himself. Either way, he still has to pay off the bank. It's likely that the bank will accept a much smaller amount, but they still have to be satisfied. If he does some backdoor shit, it could still be reported stolen by the owner or bank, the owner gets his insurance money, and buys a new bike. Then when you get caught with it, you're up shit's creek without a paddle. If he doesn't do it the legal way, the way that I look at it, it's still stolen.