This page is displayed when linked from any unrecognised site or the URL is entered directly in the address bar.
This demonstrates changing which page is presented to the viewer dependant on where the viewer has come from. This means that a comment post web link on one article can be sent to a different affiliate link than another article on the same site even though the same web address is used as the comment web link.
It has the benefit of using only one domain name instead of one for each affiliate product - this preserves your commenting persona on the blog whilst allowing you to promote more than one product from the same blog.
With this script you can also quickly change the affiliate link if one goes down or you find better affiliate product without having to change the DNS settings for the domain