As a third party you might be able to deal with the finance company and get them to proscicute the seller without loosing posession of the vehicle. If they start asking where its at though DENY DENY DENY or tell them its stripped out. If they know there is know way of getting there money back they might be willing to deal. Explain to them how much you are out and get on there side against the seller. If the buyer has to associate with the seller, he might be better off doing something else.