Plugin Reqest: Reverse Affiliate

Some of the members in my community have services (like web design and training programs) to sell. I would love to be able to have an affiliate payment link that works in reverse...where if a visitor or member of my community chooses to buy this other member's service, I get an affiliate payment.

I'm imagining this would be near-impossible, given that members might would have different payment methods and probably won't all use paypal.