Transaction management system and method

A transaction management system for managing the purchase of a product or service by a buyer from a seller, the system comprising:

• a data store for storing seller data comprising, for each of a plurality of sellers, a seller identifier;
• a program store storing processor implementable instructions;
• and
• a processor coupled to the data store and to the program store for implementing the stored instructions, wherein the stored instructions comprise instructions for controlling the processor to implement a seller interface to receive seller offer data from a seller, the seller offer data including an availability record for a product or service offered for sale, the availability record defining a plurality of periods of conditional availability, each period of conditional availability having an associated set of conditions under which the product or service is or is not available.