How do we detect the astroturfers and shills? It's pretty obvious that sites likeZDnet.com, techdirt.com and groklaw.net are targeted by some fairly well-heel

How do we detect the astroturfers and shills? It's pretty obvious that sites likeZDnet.com, techdirt.com and groklaw.net are targeted by some fairly well-heeled trolls, but what about the more subtle shills? How can we detect and banish them?