We study strategic interactions in markets where firms sell to consumers both directly and via a competitive channel (CC), such as a price comparison website or marketplace, where multiple sellers' offers are visible at once. We ask how a CC's size influences market outcomes. A bigger CC means more consumers compare prices, increasing within-channel competition. However, we show such seemingly pro-competitive developments can raise prices and harm consumers by weakening between-channel competition. We also use the model to study relevant active policy issues including price clauses, integrated ownership structures, and access to consumers' purchase data.

(joint with G. Taylor).