There are a couple of things I was wondering. Where did Harold get the instruments, uniforms, and instruction books? Shouldn't the people that made them get some of the money? If so, does this mean that he swindled them as well as the River Citizians?

Also, when the uniforms arrive, Marcellus says that the kids were in them and that Tommy was keeping them together pretending that it's a band practice. In the next scene, we see Winthrop with the adults when Charlie tells them the truth. Why isn't Winthrop with the other kids?

Don't get me wrong, I still love the show, I was just wondering if anyone had any explanations for these plot holes.

Harold Hill probably works for the company that sells the instruments. Either that, or he doesn't rip them off, but he asks for more money from the townsfolk than he uses to pay for them.

I just thought of something else. You can't ignore the fact that Harold swindled a whole bunch of other towns before he came to River City. Wouldn't there be a warrant for his arrest for his previous cons? If so, maybe he was sentenced to community service in River City and he learned how to learn music from Marion, who is the musical expert of the town.

I'm sorry, but have you SEEN the play? Or movie?

In the opening scene, the other salesmen learn about Hill from Charlie Cowell. After the train arrives in River City (after the song "Rock Island" Charlie explains that it's because of fakes like Hill that salesmen have bad reputations.
People don't know they've been conned until Hill is long gone. That was his plan for River City, but of course he fell in love and didn't leave. The plan was to sell the uniforms and instruments and instruction books, and have 'rehearsals', but be gone before anyone realized he couldn't actually teach music. Towns prior to this probably got mad that they never got an actual "band", but because they DID get the stuff they actually paid for- instruments, uniforms, books- they probably couldn't prove that Hill promised them anything or owed them anything else and would not be able to actually press charges. But, the aftereffects make the town wary and distrustful of other traveling salesmen, which is why Charlie was so mad at him.

And, as Pannic said, he probably just overcharges for the things he sells (like, the trumpets he orders cost $5, but he really charges the people $10 or whatever, and pockets the difference), and people of the small towns don't know any better- who has ever price-shopped for a trumpet? Or band uniform? The excitement he causes by getting their hopes up about a band makes them not think or worry too much about the price.