The Rakuten online shopping portal has been plagued by "stealth marketing," whereby more than 100 retailers have reportedly paid an Osaka-based firm to place fake orders and post bogus customer reviews so their products are displayed prominently on Rakuten's website.

Rakuten has sued DC8 Co., an online marketing firm that also creates and manages websites for other companies, demanding the firm pay ¥198 million in damages. During the first court hearing at the Osaka District Court on Friday, DC8 said it will contest the case.

One of Rakuten's unique features is letting shoppers on its portal rank the products they have bought in a scale of one to five stars and post frank comments. The portal also displays the bestselling products by compiling data of purchases made via the site.

According to the lawsuit, DC8, at the request of retailers selling goods via Rakuten, repeatedly made fake orders and posted favorable comments on their behalf, thus making their products show up higher on search results. As the numbers of retailers and their products featured on the portal are huge, customers tend to pick ones that show up on the first page of the long pages of products displayed.

According to several media reports, Rakuten's internal investigation found that, as of January 2014, 121 retailers who advertise their products on Rakuten's portal had paid DC8 ¥80,000 per month each to post 150 fake customer reviews that reflect favorably on them every month. Rakuten, which bans retailers from posting self-promoting comments, reportedly requested retailers to break ties with DC8, and canceled their contracts with dozens of those who didn't comply.

This is an abridged translation of a story that was first published on March 21 on J-Cast News, a Tokyo-based news site established in 2006.