The Amazon Best Seller badge, which can change from hour to hour and is based on sales and product ranking rather than reviews or ratings, is a moving target. It is crucial to regularly check that your product listing is as good as it can be for this reason.
A product with the Amazon Best Seller badge icon has the most sales in that particular category. The A9 algorithm of Amazon controls how products are shown in search results. Every hour, Amazon’s algorithm adjusts the best seller status.