Actually I do know of a few that do check sponsors from time to time - with test signups - of course it has to be blind and not set up ahead of time so its up to the affiliate to be honest about it afterwards so that they arent thought to be cheating
The other problem is that most that do shave do it on a rotating schedule so that you have to know your outgoing clicks extremely well - and know which days the sponsor has set up to not show sales - if you study it you can find the right rotation and then pick them off pretty easily. Of course of the ones Ive found I will never state it publicly as they probably do it to some and not to others - which would definitely drop my credibility somewhat
