The big picture: Amazon has banned more than half of the top 10,000 reviewers over the last two years. According to a subreddit that tracks the account deletions, 5,715 reviewers have been purged as of Monday.

The subreddit called r/TheGreatAmazonPurge tracks account deletions using a script (bot) that analyzes Amazon's top 10,000 reviewers list and registers deletions when it notices an account with zero reviews. This indicates the account has been banned or purged.

Generally, reviewers are expunged if they are caught breaking the terms of service. Most of these breaches come from by providing false reviews.

The bot has been running daily for the last two years, so it's easy to track trends in Amazon's deletion practices. For example, there was a spike in the daily rate of purges starting in late 2017 and continuing through the spring of this year.

Business Insider looked into this mass deletion and discovered a whole "subculture" where reviewers trade positive reviews for special deals and discounts.

"According to conversations Business Insider had with 29 different Amazon shoppers and sellers, a subculture geared towards driving sales through reviews has arisen on the site, and some are using underhanded tactics --- including sharing discount codes and sending shoppers free products in exchange for reviews --- to do so."

Deletions dipped during the summer, but have begun increasing again lately. Many of the banned account holders complain that they had no idea what was going on and that they never knowingly did anything against the rules. Amazon said that it would work with reviewers who thought they had been wrongly purged, but maintains that it takes review fraud seriously and is going to continue to hold "bad actors" accountable.

"We take this responsibility seriously and defend the integrity of reviews by taking aggressive action to protect customers from dishonest parties who attempt to abuse the reviews system," an Amazon spokesperson told Business Insider. "We take forceful action against both reviewers and bad actors by banning or suppressing reviews that violate our guidelines, regardless of top reviewer status, and suspend, ban or pursue legal action against bad actors, regardless of sales performance."

The review process is there to help both the consumer and the seller. Reviews help the buyer make informed purchasing decisions. In turn, they provide sellers with a way to market a good product --- the more positive reviews a seller has, the higher they appear in search results.

However, the system only works if buyers can trust the reviews, so Amazon is very strict and will not stand for fraudulent reviews. As long as everybody is honest, it's a win-win.