The Marketing Beta API is part of the eBay Buy APIs. It retrieves eBay products based on a metric, such as Best Selling. This API helps shoppers compare products and motivate them to purchase items. You can use the other Buy APIs to create a buying application that lets users, eBay members or guests, buy from eBay sellers without visiting the eBay site. The Buy APIs provide the opportunity to purchase eBay items in your app or website.