"Persona management" software allows centers of contractors to maintain the identities of these people in a rotating fashion, with the software helping the contractor to choose the right accents and vocabulary, etc.
The biggest use I've seen it in is in politics, specifically events of national security importance.
Try googling "Koch brothers astroturfing" I remember some news about their climate change astroturfing recently.
Maybe also "Tony Abbott fake twitter likes". The Australian PM was paying for twitter likes.
[1] http://wiki.project-pm.org/wiki/Persona_Management [2] https://en.wikipedia.org/wiki/Ntrepid
https://www.reddit.com/r/netsec/comments/38wl43/we_used_sock...
tldr: it's extremely difficult to detect and mitigate, relatively easy to do (assuming you have some technical skills), and quite effective
A lot also don't seem to be able to pass a Turing test but it's a very blurry line.