TradeOut.com's model is based on eBay, but is focused on business-to-business e-commerce, which, according to analysts, is the next key market. Investment banking firm Goldman, Sachs & Co., which has been one of the most active bankers in bringing Internet companies public, said it expects a five-year $1.5 trillion boom in business-to-business e-commerce in industries ranging from automobiles to medical equipment.