A system to detect outlying behavior in a network-based marketplace automatically collects attribute information for a first plurality of sellers that includes a first seller, and stores the attribute information in a storage device. The system computes peer information associated with a second plurality of sellers using a computer system, wherein the first plurality of sellers includes the second plurality of sellers, and wherein the peer information is automatically computed from the attribute information for the second plurality of sellers. The system compares the peer information associated with the second plurality of sellers with attribute information for the first seller for the purpose of automatically detecting outlying behavior by the first seller.