This paper studies the use of posted prices and auctions in a large dynamic market with many short-lived sellers and long-lived buyers. Although a reserve-price auction maximizes the expected revenue, the optimal revenue decreases when the market becomes more buyer-friendly; namely, when buyers survive longer, face fewer competitors, and become more patient. As the market becomes more buyer-friendly, the revenue advantage of a reserve-price auction over posting a price also decreases, but using posted prices would lead to sale and allocative inefficiencies.