Amazon.com has been culling book reviews from its site in recent months, though it will not disclose how many, according to a recent report in The New York Times.

The online site is attempting to crack down on authors who buy or manipulate their reviews. And writers asking family members or a fellow author to review their book is no longer an acceptable practice.

Amazon has explained its decision to remove some reviews by telling writers “we do not allow reviews on behalf of a person or company with a financial interest in the product or a directly competing product. This includes authors.”

Featured prominently on the site, reviews are crucial on the mega-shopping site that sees sales amounting to nearly a third of every dollar spent on books in the industry. Reviews are also used to help Amazon decide which books to acquire for its own relatively new publishing business.