An auction business model serves as a brokerage between buyers and sellers. According to DigitalEnterprise.org, three types of transactions may occur between buyers and sellers in a web marketplace: business-to-business, business-to-consumer and consumer-to-consumer.
In one example, eBay is a massive auction site in which consumers find products using a bidding process. The eBay business includes all three types of transactions. As a brokerage, a site like eBay charges a fee--to buyers, sellers or both--to cover the cost of bringing buyers and sellers together.