There should be an enormous amount of "buyer beware" on Instagram, or on the internet in general.
I'm not sure there is . . . a lot of people seem to believe everything they read. But there is no hope of someone policing such content, and if there was, then those people would quickly become the ones to fear, rather than the "influencers" you speak of.
EDITED TO ADD: There is nothing wrong with correcting people in public, on their Instagram feed, when they say something inaccurate. Some will adjust accordingly, and some won't.