His attention was drawn to the comments because they were heavily reported when made, and would be largely of the same structure but with a new user name each time. So he pulled up the IP they came from and all of them was made from the company owned address.
The more research one does on astroturfing and the like, the more depressing it gets. Dedicated desktop VMs running different browsers and OS's, directed through different proxies to get different IPs, etc. Where social media is involved, detailed online personas are set up for each one, with reasonable histories for using later down the track.
I think the best we can realistically do is to raise the cost of successful astroturfing/shilling to the point where it might not be economical to do, at least on a meaningful scale. As others have said, community involvement and skepticism play a huge role in that.
I was only really checking out the site because of Doctorow's stuff, and was even turned away from that as he had the annoying habit of posting random horror articles alongside his tech stuff (and the rest of the writers seemed like the typical SXSW bunch).