From a Wired article, "Herding the Mob", the concept is also called "Reputation Gaming":
"as rating systems have become more popular — and, as Resnick shows, valuable — there has been what some would say is a predictable response: the emergence of scammers, spammers, and thieves bent on manipulating the mob. Call it crowdhacking.
In some cases, crowdhackers are looking to boost sales or increase traffic to their Web sites. In other instances, they’re simply ripping off unsuspecting consumers. Either way, the more we base decisions on the wisdom of crowds, the greater the incentive to cheat. " (http://www.wired.com/wired/archive/15.03/herding.html)
"Cheats on eBay typically work like this: A scammer builds up a positive profile by selling hundreds of low-end items, then uses that high score to burn customers on big-ticket sales. That’s what police say an Arizona woman named Nancy Dreksler did in 2003. According to police reports, once Dreksler had acquired positive feedback by peddling inexpensive CDs and DVDs, she sold over $100,000 worth of nonexistent items and fled with the money, leaving more than 500 buyers empty-handed. Arizona authorities say they may yet file charges; meantime, Dreksler has pled guilty to theft and securities fraud charges in a separate Nevada case.
John Morgan, a professor at UC Berkeley’s Haas School of Business, says reputation gaming is surprisingly common on eBay. Morgan recently published a study in which he found more than 6,000 examples of buyers and sellers engaging in transactions solely to boost one another’s scores. These auctions frequently had titles like “100+ Feedback” and a price of 1 cent. Often, the item for trade was a booklet explaining how to increase feedback by reselling that same booklet.
“We saw a number of sellers who used sham transactions to build reputation, laid low for a period of time, and then reentered high-value markets as apparently ‘reputable’ sellers,” Morgan says." (http://www.wired.com/wired/archive/15.03/herding.html)