The real estate auction market was widespread in early modern Europe, but much less well known than the private sales market handled by notaries, which accounted for the majority of sales. In comparison with private sales, auction sales were designed to produce the highest possible price for a property. However, in seventeenth- and eighteenth-century France, auction sales of immovable property (either substantive property such as houses, or notional property such as rentes), through both voluntary and forced procedures, resulted in average market prices that were distinctly lower than their private sale counterparts. This article explains this phenomenon by showing that the cost and length of the auction process, as well as its highly uncertain outcome, contributed to moderating prices, as bidders added these costs to the buying price ex ante, when they did not prefer to buy outright through private sales. Moreover, the auction system, which was designed to provide optimal publicity and competition, was somewhat hampered by family rights to the property that had been seized: transfer of ownership might be blocked or annulled, even after the fact.