Both the books and the TV show. More the books because the TV show wasn't very accurate.
I think the first sneaky business lesson I ever learned was from the general store where they were advertising in the town newsletter about these big sales of 10% off everything in the store.
(Husband) Nels: We can't afford to give a 10% discount on everything!
(Wife) Harriette: Of course we can! We just increase the prices of everything 20%, then take off the 10% discount, and we make a 10% profit! And everyone thinks they're getting a great deal!
Of course the kids figured out how these merchants were ripping off the townspeople, and to get back at them, ran a "typo" in the next newsletter stating 100% off instead of the standard 10% off.
I think it's just funny that like... 20 something years later, I actually still get to see this exact same scenario happening in real life.