According to an online wiki based jargon site, the term "astroturfing" is derogatory term for misrepresenting oneself as a member of a growing groundswell of opinion. Other terms include "sock puppet" and "tentacle". The common definition covers those "paid shills" who represent themselves as part of a "grass roots" movement to support a certain belief, product, or other cause by defrauding and misrepresentation.
I am still debating whether a "Troll" or an "astro-turfer" is worse. A troll is someone who, "must be heard" and is incapable of "being corrected." They frequently post just to be heard, often about topics they are complete amateurs in. I am currently leaning towards the "astro-turfer, since he/she is a complete fraud who presents him/herself as something they are not while being paid. They are insidious and much harder to detect than the common troll. Trolls are a different story and generally much easier to detect.
But whatever the case, the internet and collaboration environments are better off without them, be they called any of the following: sock puppet, psuedo, troll, astro-turfer, etc. Beware of them all!