This paper introduces Sharing-Mart (S-Mart), an online digital trading platform developed at Princeton University to perform social file sharing experiments on top of technological networks as overlays. It describes the S-Mart system, the experiments conducted, and incentivization aspects which can be investigated using S-Mart. In the first part of the paper, the S-Mart system and the experiments conducted are explained, and the economic behaviors and dynamics of package auctions run on S-Mart are described. The major experimental observation that stands out here is that Internet users are less incentivized to share content on competitive applications, whose success depends on the co-operation of other users in the system. To alleviate incentivization issues in these applications, in the second part of the paper a mathematical framework is proposed that derives user population threshold values, which hint at the necessity of a certain base population strength in S-Mart for co-operation to take place amongst all the users. An outline of two experiments to validate the theory is presented.