E-Marketplaces are not usually studied as places for cooperative work between suppliers and buyers, involving knowledge and creation of new knowledge. The present work starts from a theoretical point of view, in order to build a model of cooperation that we have entitled "Knowledge-Based Marketplace" (KBM). e-Marketplaces catalogues proceed from a twofold problem of modelling information and knowledge from multiple points of view and from multiple experts. Buyers and sellers each bring complementary expertises to "co-construct" the catalogues. As a first step, in this paper, we justify and start to develop that model, by studying it through an experiments program of a concrete case of KBM, with a particular interest in the possibilities for new knowledge to emerge from the collaboration processes.