At the company I work for, Wool and the Gang (http://woolandthegang.com/), they are trying to realize the same idea for the niche market of hand made clothes. Basically, a `hat` will be hand-knitted by a person who is part of the `gang` and sold through the web site as a platform. However, in practice, a not so significant percent of sales come through this practice, in comparison to the traditional retail goods (such as yarn).

We use the Spree Ecommerce system for the purpose.

I know of another idea of the same sort, which is for the establishment of an online marketplace for brewery ingredients.

I guess such marketplaces are in need, for that a good alternative to the awful ebay should exist.