Before you even consider a FTF (face to face) sale, make sure that the buyer is a resident of your state and that the transaction will take place within your state. If those conditions are met, state law governs the transaction. This may range from simply trading cash for the gun, or it may involve having a dealer handle the transaction, or it may be banned altogether.
I strongly recommend that you make out a sales slip with the buyer's name and address, and get some ID to confirm it. If the gun later turns up in the wrong place, you have some proof that you sold it; otherwise, you can be under suspicion and become very close to the cops for a while, even if you never are charged or arrested. Conversely, of course, it provides the buyer with evidence that he bought the gun, protecting him if it turns out to be not quite kosher.
Jim