Vehicles are required to be titled in the buyer's name within 30 days from the date of sale. Buying or Selling a Vehicle.Get all promises about service and guarantees in writing in the contract and in the final copy of the buyer's guide. Buyer's Order or Bill of Sale the basic sales contract. Finance Agreement or Retail Installment Contract – written form of finance agreement. FEDERAL and STATE LAW requires that you state the mileage in connection with the transfer of ownership. A purchase agreement or bill of sale is required for all vehicle and trailer purchases.