So the scam is that Hill didn't tell them that without instruction, they wouldn't be able to play the instruments? Since he didn't tell them that, they were under the impression that instruments will just play themselves. I know these are simple people, but are they supposed to be that stupid?
This reminds me of an old joke: A society lady buys a violin. The seller soon receives an irate call from the lady: "You forgot to include the instruction manual!"