It's often more useful to think about incentives than try to look for evidence. Even before AI is was relatively well known that "google is dead" and you couldn't research products using google because it was all just SEO slop, so instead people were googling "X product reddit" for recommendations on like menswear, or tools or whatever they were thinking about buying. And you just think to yourself, well yeah, if I were trying to drive sales for my brand, I would be astro-turfing on reddit. And what's the incentive that reddit has to stop this happening? They don't really sell effective ads, so it's not competition, it drives engagment, and the people really responsible for stopping this (if anyone is) are the moderators, who are unpaid and so are eminently bribe-able.

Everyone understands that pretty girl on instagram who has 300,000 followers is getting paid to show that make up in her stories, why on earth would you think the guy with 300,000 karma posting his fits on /r/malefashionadvice isn't getting the same?