Here's what I mean.....
People come to my affiliate site and sign up for the publisher's e-course or newsletter...That's all fine and good except that the sign-up links in the e-mails did not have my affiliate link! LOST SALES! BIG TIME!
The lesson....always review the sales page for any leaks in your affiliate income, especially opt-ins! If there are pop-ups or areas where a reader can enter an e-mail address, then test it yourself by signing up for their opt-in with a dummy e-mail and see if the order links in the autoresponder e-mails still have your affiliate ID attached....All you need to do, is to click on the order link and if you see no affiliate code at the bottom of the order page, then you know that the publisher went around your affiliate ID!
It's also a strong reason to send your traffic to an opt-in squeeze page of your own instead of directly to the affiliate page! I haven't done this yet but am working on it right now!
P.S. It's a good idea to check all of your affiliate pages every so often because publishers will often change their pages....so there may be opt-ins or other leaks that you don't even know about!