The Andy Griffith Show (1960)

S4E26 A Deal Is a Deal

Opie and his pals fall prey to a con, unwittingly marketing a worthless skin cream. Desperate to salvage the situation, Barney and Gomer attempt to persuade the company that their product holds greater worth than it actually does. However, when their plan goes awry, everyone discovers a valuable lesson about negotiations and the importance of knowing what you're selling.