Digging up a slightly old thread - IMHO, this is the best way to process for affiliates:
1. 3rd party biller entry link, sets cookie as usual.
2. Entry also contains the affiliate ID as a variable, and this is carried over to all pages on the paysite.
3. Signup form includes the affiliate ID as a hidden variable.
4. At the billing page:
4a) If the cookie exists, use that value;
4b) If the cookie does NOT exist, use the affiliate ID variable passed by the paysite.
This way you have the cookie set by the trusted 3rd party (and the paysite cannot modify it), plus you have the hard coded variable as backup in the event that the surfer doesn't have cookies enabled.
I don't know if any 3rd party billers support this yet, I know that PSW and Verotel don't...
My new site uses internal affiliate tracking for an unusual reason - if a surfer arrives via a non affiliate link (ie - blank affiliate ID) then selected affiliates will have their ID filled in depending on which page the surfer clicks the 'join' link from.
