This is known as "selling on commission". No one should ever sell a car on commission without a cast iron contract, but the problem is that an owner may be overseas when a customer wants to buy the car. My view is that in order to buy the car you should have contact with the true owner, but if that is by phone there is no guarantee that the person you speak to is the actual owner. So you have to see a contract between owner and dealer whereby the owner assigns all rights to sell the car to the dealer and guarantees that all moneys paid to the dealer assign irrevocable rights of ownership to the purchaser.