I'm wondering what your issue is with NATS as well.
When I send hits to a site using for instance CCBill as the processor, they click on a link code with my affiliate ID but when they arrive at the site it is a plain url.
So if they bookmark the site, when they return they just go to
www.paysite.com and I lose out on the referall.
If I send it to a NATS program, when they bookmark the site the url is in the format
www.paysite.com/encodedrefcode/ and when they return I still get credit for the referall.
This adds up to a LOT.
Most people don't buy memberships the first time they visit a site. Some do, but most will either bookmark the site and buy a membership later or just type in the url next time they visit. I would estimate less than 50% of the sales come from a spontaneous referall, the rest are from bookmarks or type ins.