Every day, dozens of young men crowd into tiny rooms with 30 computers each in northern Bangladesh. Their mission: Trick Amazon.com Inc.

They open Amazon.com and repeatedly type in search terms, each time clicking on the links of products they were paid to boost, according to people familiar with the practice. Amazon’s algorithms begin recognizing that these products are popular, ranking them higher in the search results. The higher the ranking, the better chance of sales.

The scams are used to try to outsmart Amazon’s automated system that ranks some half-billion products in search results, according to interviews with consultants and businesses engaged in these practices, as well as sellers who say they have been approached by such businesses. It’s one of an ever-rotating wheel of tricks used to game Amazon’s algorithms. Some sellers pay off workers inside Amazon to gain competitive information. Others hurt rivals’ listings by barraging them with overly negative or positive reviews.

The tactics aren’t thwarting Amazon’s sales, which rose 39% in the second quarter, but they threaten to undermine the integrity of one of the world’s largest web marketplaces, which collects nearly half of every U.S. retail dollar spent online.

An Amazon spokeswoman said in a statement that those trying to abuse its systems “make up a tiny fraction of activity on our site.”