It's a big problem that there's really no safe way to do it. You just have to rely on the buyer being a good person and the only way you can get an inkling of that is based upon feedback but that's no guarantee. For very high value items, the only real safe thing to do is to trade it in to a local dealer but that means you have to find a dealer willing to take it, get less than you could get privately and buy something from that dealer.
