I see (I think). They're processing their own forms (order and payment) themselves, then, in turn, mapping the same sequence on your site. Does this mean that every time an order is made and paid on their site that they cause the same on yours? Are you getting the original customer name, addy, etc., or would you know?
Real-time detection is possibly the first goal. Unless there is something unique you can detect in the incoming 'ghost' client that you can block with, maybe you can work to detect duplicate payments, shipping addresses etc on the tail of the transaction - which assumes that your new 'partners' are ordering from you then re-shipping to their customer.
If they are taking the customer data from their own forms and re-submitting it to you, including payment (CC#?) info to you - with a markup - how are they collecting their markup? If they are collecting their full payment using the customer's payment data, THEN resending that same payment data to you, effectively double-billing the buyer, this is a much different type of problem and you should be contacting law enforcement.
From the looks of your other responses in this thread - methinks you need to do both - tech and legal. If you have a product that is inspiring so much theft/fraud, you need to protect it immediately - but not so protected that it can't be sold at all... :)