Abstract: An online computer system for bartering and trading used or surplus items stores information on used items and calculates a value for the items. The system processes a search requests for desired items and automatically notifies an item owner when a purchaser's search matches the owner's item available for sale. The system facilitates communications between the parties regarding a potential trade of the item and automatically notifies a third-party that can provide services to facilitate and support the trade. After the parties agree to a trade, the system processes a transaction for the item by transferring credit from the account of the purchaser to the account of the seller based on the calculated value of the seller's item. The purchaser's credits amount in the purchaser's account can be based on a valuation of his used items stored on the online computer system.