Clearly print or type all information, except signatures. The proof of sale for a vehicle from a dealer is the Retail Certificate of Sale (MV-50) ("Dealer's Bill of Sale").If the vehicle is purchased from a New York State dealer, provide form MV-50 (Retail Certificate of Sale). An RV Bill of Sale is a legal document that serves as proof of the sale and transfer of ownership of a recreational vehicle (RV) from a seller to a buyer. This is typically one of the first items you'll put on the bill of sale.