Umm, the people in any scam voluntarily buy the thing they've been duped into buying. It sounds like you're just trying to argue the point so you "win". Even to the point of flying into absurdity.
The point isn't "oh, we're buying this thing cause it has the American flag on it.", because of that were the case, that would be totally ok.
The problem is that the person selling is doing so buy whipping their customers into a frenzy of "patriotism" where they're convinced that the person speaking is some warrior for their freedoms and that they should be too. While in such a frenzied state, they put near absolute trust in the speaker, who then abuses that trust to sell merchandise.
To be fair, this is nearly identical to how most YouTubers make their money. The difference being, however, that a normal YouTuber isn't coaxing their viewers into a froth-at-the-mouth rage mode over the premise that their country is under assault from threats that are pretty much made up, based on the prior threats that were similarly fictional.
To put it to an extreme example, one of the most prolific of these grifters, Alex Jones, convinced an entire audience that he had a cure for COVID-19. He did this through first coaxing his audience into the idea that the doctors were all liars and that he himself knew the secrets (which of course, he vaguely referred to and never once presented). The "cure" of course, was fake.
This is the most extreme example, of course, but the other grifters are far more subtle. Rather than selling obviously fake medicine, they choose to sell hats, pins, books, and coat tags. All those things with, as you mentioned, the American flag emblazoned prominently.
These grifters are not patriots. They do not actually care about a single word they say. They only care to make money, and using the above technique, they quite often make a ton of money. In fact, it makes so much money that Trump himself used a version of this "frenzy before sales" technique to rake in an unprecedented amount of campaign money. Much of which was never used on the campaign.
Do you understand now?