B2C2C

External Entities interfacing indirectly with e-marketplace 

B2B Home 

Though B2C (Business to Consumer) and C2C (Consumer to Consumer) sites are not a part of the e-marketplace, they may have interfaces with the e-marketplace.

B2C 

A B2C site could be a company owned web site reaching out to its own customers, like the Sun Store;  Or may be a portal serving as a platform to let business reach out to a common set of customers, like Indiatimes B2C portal.

In the first case, where the B2C site serves a single company, the site can directly link to the company's own enterprise back-end system (ERP modules like CRM and order processing systems).

Whereby in the second case, of a B2C portal, serving a common pool of customers by connecting them with multiple businesses, it makes more sense to integrate the B2C portal directly with the e-marketplace. 

The B2C portal connectivity with e-marketplace saves cost by having only a single gateway from which the portal connects back to multiple participant businesses. Also, the e-marketplace participants can get access to multiple B2C portals from a single gateway, saving then resources and time to connect to multiple B2C portals.

The above scenario can only be achieved through a federated identity and trust relationship, like the Liberty Alliance Project.

C2C

Most of the B2C portals like Ebay and Amazon have evolved into a C2C platforms. They also promote community building around their portals. The community provides the portal with customer "stickiness" as well as helping in building mutual trust relationship for informal rating and recommending of the sellers.

 e-Communities

Many marketing oriented communities sites like Squidoo have promoting e-commerce, make money through their members' recommending to buy from the B2C and C2C portals. They create referral relationships with e-commerce portals and make it easy for their community to earn rewards for recommendations. However, the commissions earned from the actual sales is shared by the B2C site as well as the community site.

Other pure play communities like Tribe do not (yet) have an  easy way to monetize recommendations.

Communities build around the B2B marketplace can have an informal rating system based on mutual trust as well as have mechanisms to monetize referral, without a third party intermediation.