Season 1's "Art and the Addams Family" is really bad. Specifically, it's an unfunny, structurally nonsensical bore, with a very annoying antagonist. This is where we meet Sam Picasso, who also appears in "Morticia, the Sculptress." That episode is a slightly better remake of this one, which is just miserable. Grandmama has taken to painting, but is quite bad at it. To help her out, Gomez tries to hire Pablo Picasso. Instead, he gets a con man named Sam.
Poor and starving, Sam visits the Addamses and is (of course) horrified by them. That's the joke — he spends the entire episode afraid. Each attempt to help him relax just makes him more frightened. It turns out that Wednesday is an okay painter, but Sam gets all the credit for it. That's how this episode ends: A guy lies to the nice people who give him food, money, and a place to stay, then takes credit for their daughter's work. Now, the joke could be that the Addams family is just too quirky to notice or care that they're being had, but that's a pretty weak punchline to an already boring episode.