As traditional commerce moves on-line more business transactions will be mediated by software agents, and the ability of agent-mediated electronic marketplaces to efficiently allocate resources will be highly dependent on the complexity of the decision problems that agents face; determined in part by the structure of the marketplace, resource characteristics, and the nature of agents’ local problems. We compare auction performance for agents that have hard local problems, and uncertain values for goods. Perhaps an agent must solve a hard optimization problem to value a good, or interact with a busy and expensive human expert. Although auction design cannot simplify the valuation problem itself, we show that good auction design can simplify ...