It's bloody difficult.

I used to mod on /r/videos years and years back. We had this one guy who was not very active as a mod in the day to day stuff, but was respected because he'd basically disappear for a few months and then reappear with a huge post in our modding sub basically going "so these are all spammers/malicious actors, here's their profiles, the accounts were created in these waves, here's where they've copied existing posts / the identical generic comments and things they use to get around our posting requirements, the targets they've been promoting, etc". Just huge pages of thoroughly researched proof.

This was well before we had huge awareness of situations like Russia manipulating social media - it was usually those viral video places that buy up rights to videos and handle licensing and promotion. It's why for a long time any licensed videos from places like viralhog etc were outright banned - they were constantly trying to manipulate reddit postings in bad faith, and even trying to socially engineer the mod team in modmail, so any videos that mentioned a licensing deal in the description were automatically banned from posting.

If we didn't have that one guy spotting the patterns, most of it would have gotten by easily. Unfortunately he did eventually disappear for good. No clue what happened to him, hope he just cut out social media or something. But with the spamming and astroturfing stuff... Even after fighting it for years I can't tell you what to do to counter it besides "have more of that guy".