1. A computer-implemented method comprising: receiving item data at a machine of a network-based computer system, the item data related to an item categorized in at least a first category of a plurality of categories supported by the network-based computer system and including an item price-based value associated with the item; determining a category-specific threshold price-based value of the first category; automatically determining at the machine that the item data is irregular, based on the item price-based value and the category-specific threshold price-based value; and responsive to the determination that the item data is irregular, causing the machine to restrict an entity associated with the item from using the network-based computer system.