Buy.com reported 146% year-over-year sales growth for its retail Marketplace, which currently has more than 11.5 million product listings from thousands of third-party sellers. Buy.com's Marketplace comprised 46% of orders in the fourth quarter of 2009 and more than 50 percent of orders in the first quarter to date.

The Buy.com Marketplace initially offered consumer electronics and technology products and has grown to 20 product categories, including games, apparel and shoes, books, bags and luggage, fragrance, home and outdoor, software, sporting goods, jewelry and watches, toys and baby goods, and more. In December 2009, Buy.com added name-brand retailers including Tiger Direct and Paul's TV.

It is becoming increasingly difficult to separate partners from competitors in the ecommerce industry, where sellers are marketplaces and marketplaces sell on other marketplaces. In addition to offering its own listings on multiple channels and opening its own site to third-party sellers, Buy not only sells on eBay, it has also begun cherrypicking Powersellers to sell on its Marketplace. And, Buy.com let another marketplace onto its site: in December, it welcomed Alibris, a marketplace for independent sellers of new, used and rare books.

Buy.com CEO and President Neel Grover said, "As we move into 2010 and beyond, Buy.com has transformed from an online retailer with marketplace functionality, to a multi-category retail marketplace platform. We firmly believe that our marketplace platform is the future of online retail."