Direct marketing is witnessing explosive growth. As consumers increasingly purchase products from their homes, their ability to judge the quality of products they buy is significantly reduced. In this paper we study how money-back guarantees can signal product quality in such environments. We interpret product quality broadly to mean both the level of attributes promised as well as the firm's consistency in delivering on those promises. Key aspects of our formulation are the explicit consideration of transaction costs, and alternative signals of product quality. Transaction costs are the costs the seller or buyer faces when redeeming a money-back guarantee. We show that money-back guarantees signal quality by exploiting the higher probability of returns for a lower quality product, and the attendant higher transaction costs. However, if the seller's transaction costs are very large, then there are less costly ways to signal, namely charging a high price. We compare the signaling performance of (1) price, (2) price with uninformative advertising, and (3) price with a money-back guarantee. Whereas uninformative advertising does not work at all in our model, under certain conditions a money-back guarantee is necessary to signal, and under other conditions, a money-back guarantee is a useful supplement to price.money back guarantee, warranty, signaling quality, transaction costs, separating equilibrium