Ah, my bad. So it's affiliate marketing. I guess my question to you would be what defines a lead? If it does not have a dollar value tied to it, then yes there's always a chance you could be duped. You could always track the ip number of persons generating a lead. If they're all in similar locations, or several leads coming from one ip, you know it's fraud.
I think that PDF is helpful. If you have a website analytics programs you should be able to get your questions answered.
Hope that helps.