An electronic commerce system includes a broker that enables customers to purchase items from merchants. A customer interacts with the merchant to identify items to purchase, and the merchant directs the customer to the broker in order to complete the transaction. The broker receives a description of a virtual shopping cart generated by the merchant and presents the customer with an interface allowing the customer to select shipping and other options for the purchase. The broker calculates a total amount for the transaction based on the shopping cart description and the options selected by the customer. The broker informs the merchant of the purchase and coordinates the shipment of the purchased items from the merchant to the customer.