multisite marketpress with affiliate programs

Hi

sorry about the question title as I didn’t know how to word it. But my question is, and this maybe stupid but I just need to confirm it, when I have a multisite with marketpress enabled where customers can open stores of-course with the use of pro-site. And I allow Paypal chain payments so that I get a cut of the sales. Now what if one of the customers opens a store and fills it with affiliate products eg amazon, from my understanding is that in this case I won’t be able to get a cut as the transaction is done in amazon, So how will I be able to get around this especially if I allow my customers to open a store for free for the purpose of only getting a percentage of their sales.

sorry for the wording of the question in advance

any help would be appreciated

Thank you