When ever I have sold a car I inform the buyer that if they want the car I will need a bill of sale and a un-refundable deposit, otherwise it is first come, first serve. When ever I have purchased a vehicle I inform the seller that if they want to sell the car, I will need a bill of sale and I put down a deposit. Sorry that you missed out on the car, sellers always want to keep their options open, and nothing is final 'till the paperwork is made.