The problem is particularly pronounced in China, according to the report.
Fake customer reviews written by the merchants themselves were also among the probe's chief concerns, the company said.
Amazon's vast marketplace is ripe with manipulation from unscrupulous third-party sellers trying to gain better rankings.
Amazon said it is investigating reports that some employees took bribes to leak internal data and alter negative product reviews on its website. "And then the contractor that they hired would leave a glowing review for each of those products that they sent out", clarified Alex Goldman, host of Reply All, as per Mashable.
Hand over detailed search data.
Amazon is investigating reports that its retail employees are selling internal data and reviewers' email addresses to merchants that want to game the system. Should attempts to reconcile negative reviews fail, the market rate for removal services is around $300 per review with a typical minimum order of five take-down requests.
Amazon's internal investigation into the matter began after the company was tipped off in May about the practice.
Because most online shopping searches now start at Amazon, rather than at a search engine, virtually every retailer and manufacturer that wants to reach people online has little choice but to set up shop on Amazon's platform.
Following the report, Amazon said that it has "zero tolerance" for such abuses and that it was conducting a "thorough" investigation into the allegations. This includes terminating accounts, deleting reviews, withholding funds, and taking legal action.
It would also "take legal action" should it be required.
But according to The Washington Post - which is owned by Amazon founder and CEO Jeff Bezos - "Amazon's ban has not cut down on paid reviews so much as pushed them into the shadows, say sellers and researchers". The service is generally used to connect sellers with Amazon employees for help with their accounts.
Workers at the internet shopping giant's distribution centers face disciplinary action if they lose a punishing race against the clock to track down items ordered by online shoppers.