An e-commerce system is provided that tracks purchase transaction across multiple client devices. The e-commerce system stores hop information describing when a customer is exposed to a product of a vendor through an affiliate who advertises the vendor's products. The e-commerce system determines from the stored hop information which affiliate or affiliates to compensate for the sale of a product. This allows the e-commerce system to determine, after the sale, whether additional affiliates need to be compensated for the sale of the product based on the hop information.