The counterfeiters buy legit products and return their cheapo fakes through fake buyer accounts. So for the price of manufactoring the counterfeit products they’ve purchased the real thing.
They then sell the authentic products through other channels and appear to be supplying authentic, quality products affordably to buyers and marketplaces while at the same time poisoning the legitimate market.
It’s essentially counterfeit laundering.
Advertisements should be explicit. You’ll often see sponsored segments of videos when a YouTuber is talking about a product, where they explicitly say it’s sponsored. These influences are being asked to treat the product preferential to other devices without being a sponsor.
Advertising is one thing. Asking people to advertise your product without revealing that it’s an ad is something else.