I've seen similar suspicious patterns on Amazon and eLance.
I discovered what appeared to be suspicious clusters of Indian accounts in particular, on eLance, all with ridiculous project descriptions, that are then all seemingly awarded to other accounts within the same "circle", racking up huge US dollar fee amounts in project awards, very quickly, with lots of suspicious mutual account birth timestamps (where both the project awarder and the project winner both seem to join the site on the same day, award a project to the other very soon thereafter, etc.). Shame that people engage in practices like this. Adds a lot of noise, drowning out signal. I've pretty much given up on using any low-bar-to-participate crowdsourced opinion site, and eLance-like sites, due to this phenomenon.
I'm also reminded of a guy I once worked with, who never seemed to do anything or deliver anything real, and yet has something like 50+ recommendations on LinkedIn. A talker/political kind of guy -- a middle manager. Whereas I know another guy, same company, who was super productive, heads-down coder, effective, delivered, innovative, very smart, solved lots of very big and very real technical problems while at that company, and he had like 1 LinkedIn recommendation -- an engineer, of course. You just know the first guy was offering "scratch my back, I scratch yours" deals to his mutual recommender buddies (assuming all of them were even real people), whereas the second guy was quiet, non-political, non-slimy, honest and humble. Again, any sort of crowdsourced opinion or social network voting system can and WILL be gamed, driving the signal to noise ratio down.
Solving this problem in general, in my opinion, is/was right up there with solving the spam problem for email.