There are estimated to be more than 300 companies in China creating fraudulent app reviews

"An industry insider said recently that there were at least 300 companies in China specializing in submitting fraudulent reviews for applications. The insider said that at a conservative estimate 30% of mobile applications used the services of these companies, and that 70% of applications had boosted their app rankings either using their own staff or the services of these companies. The practice of hiring people to boost app download figures and positive ratings, and to leave negative feedback for competitors' applications, is an open secret in the industry."

Source:  China Business News, via Marbridge Daily, 9th February 2012