A key issue for the design of online marketplaces is addressing leakage. Buyers may use the marketplace to discover a seller or to obtain certain conveniences, but the seller may then want to take transactions off the marketplace to avoid transaction fees. Assuming buyers are heterogenous in their switching cost or inconvenience cost of purchasing directly, we provide a model in which there is partial leakage in equilibrium. We use the model to analyze the tradeoffs associated with different strategies the marketplace can use to attenuate the effects of leakage: investing in transaction benefits, limiting communication, charging referral fees, using price-parity clauses, introducing seller competition on the marketplace and hiding sellers that try to induce too much leakage.