In a marketplace model, the notion of supplier is taken over by the seller. These two very distinct notions illustrate the change in business model between e-commerce site and marketplace operator. With an e-commerce site, you work with a supplier, and sales prices are set according to the rates negotiated by your purchasing teams. You manage your product catalogue, storage, delivery and customer relations.
In a marketplace model, you are the intermediary between the end customer and the seller. The seller is independent in setting their pricing policy, choice of catalogues and development of product fixtures. They define their own delivery policy and manage their own inventory.