Two types of agents itneract on a pre-existing free platform. Agents value positively the presence of agents of the other type but may value negatively the presence of agents of their own type. We ask whether a new platform can find fees and subsidies so as to divert agents from the existing paltform and make a profit. We show that this might be impossible if intra-group negative externalities are sufficiently (but not too) strong with respect to positive inter-group externalities.
Belleflamme, P., & Toulemonde, E. (2009). Negative intra-group externalities in two-sided markets. International Economic Review, 50(1), 245-272. https://doi.org/10.1111/j.1468-2354.2008.00529.x (Original work published 2009)