Ever wonder who are the people pumping out consumer reviews for books, music, movies and restaurants and hotels on online sites like Amazon.com, Yelp and TripAdvisor?

The New York Times takes a look at the world of online reviews as more and more sites depend on their kind, five-star ratings to compete in a crowded “social” shopping space. That demand has spawned “an industry of fibbers and promoters has sprung up to buy and sell raves for a pittance,” according to the article:

With intense competition on line, the NYT article says that “boundless demand for positive reviews has made the review system an arms race of sorts. As more five-star reviews are handed out, even more five-star reviews are needed. Few want to risk being left behind.

Companies like Amazon are concerned about the integrity of the reviews. But they also are doing their best to keep the pipeline of good reviews flowing.

Cornell University researchers, meanwhile, recently conducted a survey of the top thousand customer reviewers at Amazon.com. In their study (pdf, 90 pages), the researchers tackled one big mystery:

Given that Amazon is the world’s largest online retailer why is it that so many people work, in effect, for free for Amazon by providing content for the website for no remuneration? Is this even true?

Amazon was one of the first online retailers to realize the importance of allowing its users to post their own reviews, according to the study.

The reviews from “ordinary” people are more credible to some consumers, who tend to trust peers who have used a service or product over a slick marketing campaign from a company selling something.

The study concludes that the top reviewers are motivated by a sense of community. They “derive a strong sense of identity from their reviewing activity – they really care about their rank and reputations.”

The study warns, though, that the credibility of customer reviewing is at risk:

But all is not pure in the top-reviewers’ world. Reviewers are increasingly rewarded with free books, reviews are directly solicited, there is the possibility of gaming the system, and in order to maintain their ranking, a level of productivity is demanded that seems to go against the grain of serious book reviewing. Reviewers, especially the more prolific ones, are starting to cut corners and find ways of upping their productivity.

And the study also says Amazon faces more challenges to the credibility of its reviewers as the gushing posts expand to cover other retail lines:

Perhaps other items such as toothpaste, baseball caps, post its, and printers could eventually spawn a similar culture of taste but it would take time and for sure someone who is the arbiter of taste in books is unlikely to be the arbiter of taste in light bulbs. The conceit Amazon has, that all products can be sold the same way, may be correct, but a reputation system that levels the playing field such that a reputation for reviewing light bulbs is commensurable with one gained from reviewing a work of literature runs the risk of one day being exposed as a sham.