Brokerage

Brokers are market makers: they bring buyers and sellers together and faciliate transactions.
Monsieurprix uses this kind of business model (as a pure one).
http://www.monsieurprix.com/
The website proposes many products at many different prices. With the use of a filter, the customer can choose what he prefers. With a link system, monsieurprix redirect the customers to the seller's website. The seller must pay a fee to monsieurprix in order to be catalogued on it.