This also is absolutely rampant on reddit in the past months.
I think the turning point was when they allowed accounts to hide their comment history. Before, when you could click on an account and read all of their other comments it was easy to tell when an account only existed for fake conversations about a product they were spamming.
Now the spam accounts hide their comment history so they can do nothing but spam similar comments all over Reddit and walk the line where it’s not obvious if any single comment is spam or an one off comment from someone trying to be helpful.
Users are using Google and other services to find their other posts and post warnings, but it takes so much more effort now.
It's maybe account laundering, but on any popular post you'll see at least half of the comments are tangential at best. They're not an expression of anything a person would express, like replying with just skull emojis to a random news post, or saying "he really said" with an exact word to word recreation of a throwaway quote from a video. No one ever replies to these posts, they get like 2 upvotes (if that), the platform doesn't reward them at all but they constantly appear in a very artificial looking way.
The advantage of hiding one's comments is precisely that they do not show up as easy as before on Google, discussions don't get derailed because of comment muckrakers going through their opponent's post and accuse them of being anti-zionist or pro-zionist, and actual stalkers have a far more difficult time tracking down victims.
The reliability of reddit comments has been questionable even before LLMs. Because people trying to push whatever they are interested in pushing realized that having organic-looking comments is the perfect way to sway people who don't trust professional publications and traditional ads. And now with LLMs in the mix, there's basically not even a cost to doing this and making it look like tons of people love your product and are sharing their friendly thoughts and advice.