We illustrate conditions under which a trade platform selling its own products alongside third-party sellers benefits or harms consumers. This benefits consumers by lowering prices in a suite of models: a gatekeeper platform facing a competitive fringe of sellers, when fringe sellers also have...

Equilibrium prices behave quite differently if consumers single-purchase (buy either Time Magazine or Newsweek) or if some consumers multi-purchase (buy both). Prices are strategic complements under single-purchase, and increase with magazine quality. In a multi-purchase regime prices are...