Just for your own peace of mind, although its not required by law, you might ask if they have an LTCH. If they do, then you know they've been checked out to be a "good guy". If I were doing a face-to-face in the Walmart parking lot, I would ask for an LTCH and a driver's license and make sure the info matches up, and check that the buyer is 18 or older. If they don't have an LTCH, you might consider using the services of an FFL for the transaction just to be sure you are selling to a good guy. Again, that is not a requirement for a private transaction, it just gives you the peace of mind of knowing you are selling to a "proper person".
Also, for a face to face transaction with a stranger, you might want to bring a friend along for safety.
Also, for a face to face transaction with a stranger, you might want to bring a friend along for safety.