I'm not the original poster, but I do believe that astroturfing of social media is a reality of our world. The only real source I can provide is http://www.bbc.com/news/uk-31070114

And point out the fact that many companies hire social media people. I can also point out old cases like https://i.imgur.com/LY5suhh.jpg

I'm not sure I'm as paranoid as op, but if you think that no agency has at least seriously experimented with this stuff (instigating flame wars etc.) then remember how you felt reading the few people saying "they're recording everything you're doing on the internet".