Who processes the payments? How do I know how timely the order has been received by you and sent on to me?
Probably a better way to manage this might be to somehow add the products to a cart, then at "checkout," pass the entire cart to my payment page with a variable for an affiliate id. This way "my" credit card processor manages the payment, and both you and I know the specifics of the order without anyone having to manually pass anything along.
Or when they are "adding to cart," it adds to a cart system on my site in the first place, then redirects any "keep shopping" back to your site.