Season 1: Episode 2: The Lisa Card
Most kids would see a credit card as a responsibility, but most kids don't have a shopping addiction as big as Lisa Turtle's. Lisa's dad doesn't mean any harm when he offers his credit card to Lisa as a reward for her good report card, but when she spends too much she realizes she's in trouble. Zack sells her clothes to help her earn money to pay off the bill. It's amazing that Zack didn't want commission for all his sales.