It seems that most internet marketers already know about Clickbank products so when they need to buy it, they would just replace your referral link with their own Clickbank ref link to make a purchase so they spend much less to get the product. Is this happening to you?
I'm sure it happens all the time. That's why I don't sell things to other marketers/SEOs. They know the game. Why don't you try selling things to everyday people who don't know what an affiliate link is?
You can always cloak your affiliate links and make sure that the URL is kept in the browser when you redirect them. I know you can do that with EasyTrackerPro. I guess some will figure it out anyways, but it could be worth a shot