Affiliate system

Hi guys, I am reviewing an affiliate system that I created a while ago. I am using a very simple method to do this, but I am curious if there is any better system (better I mean less missed affiliate purchases). 1. User click on affiliate link http://thedomain.com/?a=1234 2. The if $_GET['a'] is set, we check if that is an valid affiliate, and then set a cookie for that 3. At purchase, we check if that cookie still is there, if so, we register it as a affiliate purchase and that info is stored in the purchase database What should I do if they do not allow cookies? I could amend a=1234 onto every url that they pass, but that would not be a "beautiful" solution. Maybe I can also create a SESSION that stores the affiliate information so that it at least get registered if the purchase is completed within the session? What do you think is the best way? Best regards, Peter Lauri www.lauri.se - personal web site www.dwsasia.com - company web site