Legal Question in Credit and Debt Law in Pennsylvania

There is no such thing as a "gentleman's agreement" today. Get it in writing next time.

You sold him a car - did you keep a lien on the title? If so, you would have some protection. If not, did you at least do a proper bill of sale indicating the purchase price of the car and note that he paid you money but not all? Did he make any payments to you by check and write something in the memo line liuke "for car loan installment"? If not, the texts make work to prove that he owes the money.

You can take him to small claims court (assuming he lives in PA - if not, small claims in the state where he resides if you are close to the state). You will probably recover a judgment against him. But it will be hard for you to collect on it, but it depends on what he owes.