I would get a bill of sale with PO name address, your name and address, purchase price and date of sale. Signed by the PO yourself, and a witness or two. When I took my paper work to the DMV, they asked how much I paid, and had to pay sales tax on that amount. I was kind of shocked because I've bought used vehicles from private partys before and just had to pay a small amount in taxes. NOT this time. About 6 weeks later I get a letter in the mail from the state of ILLINOIS stating I didn't pay enough sales tax because they didn't feel I disclosed the correct amount I paid for the vehicle, and stated according to their figures I owed x amount more. Their figures were full retail, I paid $10,000 less. It's a good thing the PO had this bill of sale made up and required me and my buddy to sign his copy and my copy before I left the premises. I thought that was way over kill at the time, but when the state pulled that on me I'm glad I had that bill of sale.