What is the Buy Box?
The Buy Box is the display on a product detail page with the Add to Cart button that customers can use to add items to their shopping carts.
When one of your listed items appears as the default on the product page, you “win” the Buy Box, increasing your chances of selling that item.
Becoming eligible to win the Buy Box doesn't guarantee that you will win it; that said, there are a few things you can do to increase your chances. The "Buy Used Box" is not available in many categories, and availability is subject to change at the category's discretion. To learn more, see Winning the Buy Box
How can I become eligible?
You must meet all of the conditions listed below to make your offers eligible to win the Buy Box. In any case, Amazon does not guarantee placement in the Buy Box.
Type of selling account: You must have a professional selling account. Here's how you can check your current account type and upgrade, if required.
Your Order Defect Rate, Cancellation Rate, and Late Shipment Rate are metrics that determine eligibility - the better you perform, the higher your chances are of becoming Buy Box eligible.You can see how you are doing on the Account Health page.
So that Amazon can accurately assess your performance, we require that you have sufficient order volume (which varies among categories).
Your offer using a Fulfillment by Amazon (FBA) might have better chance to be eligible to win the Buy Box as such offer uses shipping and customer service by Amazon and may achieve better results in 2. Performance Metrics.
Please note that the product page might not have the Buy Box if there is no offer priced competitively.