Check to see it has a clear title. In Florida it needs a title to be re-registered...Be sure all numbers match and he signs the title and get a signed receipt, for tax purposes. If he doesn't have the title have him go to DMV,(Dept. of Motor Vehicle) and get one. It's easier for the owner to get it than you. Plus he can pay the fee for the title too.
(I'm a certified Florida Car Dealer)
Karl
(I'm a certified Florida Car Dealer)
Karl