1. A method for executing marketing campaigns, the method executed by a computer system comprising at least one computer, the method comprising: receiving, via a computer interface provided by at least one computer, information for a marketing campaign associated with a supplier of items, the information for the marketing campaign including a promotion for an item of the supplier and execution criteria defining circumstances under which the promotion should be presented to a user via a computer network site; receiving, via the computer interface provided by the at least one computer, forecast data for the supplier, the forecast data computed based on future availability of one or more items provided by the supplier; modifying, by the at least one computer, the execution criteria of the marketing campaign based on the forecast data; responsive to receiving, from a client device, a request for an item, determining whether conditions associated with the request satisfy the modified execution criteria of the marketing campaign; and responsive to satisfying the modified execution criteria, automatically determining whether to transmit the promotion for presentation on the client device.