ELECTRONIC COMMERCE SYSTEM UTILIZING CUSTOM MERCHANT CALCULATIONS

A customer interacts with merchants to identify items to purchase, and the merchants provide virtual shopping carts identifying the items to a broker. The cart requests that the broker utilize custom merchant calculations for the transaction, such as for determining shipping costs. The customer interacts with the broker to identify customer information, such as a shipping address, and to purchase the items. The broker sends the customer information to the merchant and requests that the merchant perform the custom calculations. If the merchant provides a valid response to the request, the broker uses the merchant calculations to calculate the total price for the transaction. If the merchant provides an invalid response, the broker utilizes backup calculations specified in the cart to calculate the price.