I read through this, and all I heard in my head was "Click Here to receive 10% off your next purchase" and then the repeated sound of old-school cash registers.

I read through this, and all I heard in my head was "Click Here to receive 10% off your next purchase" and then the repeated sound of old-school cash registers. I think the hardest part would be coming up with an adequate monetization strategy for the purchasing sites. It may be a long-shot, but you may be able to do something like, user submits a referral. Referral receives a potential discount, original user can now redeem the discount promised. Your company receives x% of the purchase by the user using the discount. The existence of your service basically garnered 2 extra sales for the site, but I think it would be difficult to charge based on just the usage of the service. I think it would be an easier sell if you only charged if the referral resulted in a purchase. That way it costs the company nothing to try and get the free sales. The problem is, the take rate may be completely out of balance for the loads. Either way, done right it sounds like it could benefit the seller, the buyer, the referral and you, which is usually a pretty good sign of something worth trying.