Misuse of ratings, feedback, or reviews: Any attempt to manipulate ratings, feedback, or reviews is prohibited.
Ratings and feedback: The rating and feedback features allow buyers to evaluate the overall performance of a seller, helping sellers to develop a reputation within the Amazon Marketplace. You may not post abusive or inappropriate feedback or include personal information about a transaction partner. This also includes posting ratings or feedback to your own account. You may request feedback from a buyer, however you may not pay or offer any incentive to a buyer for either providing or removing feedback.
Reviews: Reviews are important to the Amazon Marketplace, providing a forum for feedback about product and service details and reviewers' experiences with products and services—positive or negative. You may not write reviews for products or services that you have a financial interest in, including reviews for products or services that you or your competitors sell. Additionally, you may not provide compensation for a review other than a free or discounted copy of the product. If you offer a free or discounted product, it must be clear that you are soliciting an unbiased review. The free or discounted product must be provided in advance. No refunds are permitted after the review is written. You may not intentionally manipulate your products' rankings, including by offering an excessive number of free or discounted products, in exchange for a review. Review solicitations that ask for only positive reviews or that offer compensation are prohibited. You may not ask buyers to remove negative reviews.
Misuse of sales rank: The best seller rank feature allows buyers to evaluate the popularity of a product. You may not solicit or knowingly accept fake or fraudulent orders. This includes placing orders for your own products. You may not provide compensation to buyers for purchasing your products or provide claim codes to buyers for the purpose of inflating sales rank. In addition, you may not make claims regarding a product's best seller rank in the product detail page information, including the title and description. Source: https://sellercentral.amazon.com/gp/help/200386250