Brokers are market-makers: they bring buyers and sellers together and facilitate transactions. Brokers play a frequent role in business-to-business (B2B), business-to-consumer (B2C), or consumer-to-consumer (C2C) markets. Usually a broker charges a fee or commission for each transaction it enables. The formula for fees can vary. Brokerage models include:
Marketplace Exchange -- offers a full range of services covering the transaction process, from market assessment to negotiation and fulfillment. Exchanges operate independently or are backed by an industry consortium. Orbitz, ChemConnect
Buy/Sell Fulfillment -- takes customer orders to buy or sell a product or service, including terms like price and delivery. Carsdirect , Respond-Com
Demand Collection System -- the patented "name-your-price" model pioneered by Pricelinecom. Prospective buyer makes a final (binding) bid for a specified good or service, and the broker arranges fulfillment. Priceline-Com
Auction Broker -- conducts auctions for sellers (individuals or merchants). Broker charges the seller a listing fee and commission scaled with the value of the transaction. Auctions vary widely in terms of the offering and bidding rules. eBay
Transaction Broker -- provides a third-party payment mechanism for buyers and sellers to settle a transaction. PayPal, Escrow-Com
Distributor -- is a catalog operation that connects a large number of product manufacturers with volume and retail buyers. Broker facilitates business transactions between franchised distributors and their trading partners.
Search Agent -- a software agent or "robot" used to search-out the price and availability for a good or service specified by the buyer, or to locate hard to find information.
Virtual Marketplace -- or virtual mall, a hosting service for online merchants that charges setup, monthly listing, and/or transaction fees. May also provide automated transaction and relationship marketing services. zShops and Merchant Services at Amazon-com
for more info: http://digitalenterprise.org/models/models.html