Amazon is restricting users from posting reviews of former FBI Director James Comey’s new book, A Higher Loyalty: Truth, Lies, and Leadership, unless the reviewer has purchased the book through the retailer.

Deadline noticed the issue, noting that the restriction is in place for the print and Kindle editions, and that some low-rated reviews might have also been removed as well. A review on audiobook platform Audible, which is owned by Amazon, complains that the user’s prior review had also been removed. We’ve reached out to Amazon and Audible for comment, and will update this post if we hear back. Barnes and Noble doesn’t appear to have any such restrictions for its reviews, and its reviews include a number of anonymous one and five starred reviews.

This isn’t the first time that Amazon has restricted reviews for high-profile books: the company deleted a number of one-star reviews of Hillary Clinton’s book What Happened and Michael Wolfe’s book Fire & Fury: Inside the Trump White House following their publication, under the suspicion that they were published by opponents. Amazon’s Community Guidelines state that it will restrict non-Amazon Verified Purchase reviews for products when the company detects an “unusually high numbers of reviews for a product posted in a short period of time.”

That policy makes sense, given that high profile books for controversial figures can become the target of opponents or supporters who wish to affect the book’s overall rating. Rating gaming is a thing that happens from time to time. Earlier this year, a Facebook group called “Down With Disney’s Treatment of Franchises and its Fanboys” claimed that it was behind low ratings for Star Wars: The Last Jedi on Rotten Tomatoes and planned to conduct a similar review-bombing campaign before it was shut down by Facebook, while in 2015, Chuck Wendig’s Star Wars novel Aftermath was similarly the target of negative reviews on Amazon.

Amazon’s vast storefront means that it would be difficult under any circumstance to examine each and every review that comes in to ensure that it’s complying with its Community Guidelines. Accordingly, there are some basic restrictions to tamp down abuse: the site prohibits users from contributing false or misleading reviews, while publishers and authors aren’t allowed to buy reviews to game the system. Indeed, Amazon’s “Verified Buyer” identification is a useful check on attempts to game the system: allowing the company to filter out reviews for high-profile books in some cases, while also restricting users from posting more than five non-verified purchases a week. But that restriction can be annoying for someone who’s purchased the book from a non-Amazon source, but who wants to contribute to the larger body of reviews on Amazon. In all likelihood, they’ll just have to wait for the fervor to die down before they can post their thoughts.