1. A method for guaranteeing a consumer a best price on an item purchased from a vendor in a consummated final first transaction at a first price, the method comprising: recording the first price and information identifying the consumer; monitoring a sales price of the item for a predetermined time period after purchase of the item by the consumer in the consummated final first transaction; noting any price lower than the first price for the item during the predetermined time period following the purchase of the item; calculating a money-value difference between the first price and said any price lower than the first price; and refunding to the consumer a refund amount equal to the money-value difference, wherein the item is purchased via a host system and the host system records the first price and information identifying the customer; the host system conducts the monitoring, noting, and calculating steps; and the host system provides the refund to the consumer, wherein the host system provides the refund by crediting an account of the consumer, wherein only prices for the item to be sold by the vendor involved in the first transaction are taken into account in the noting step; and displaying the refund amount.