I don't know exactly how AdSense / YPN works, but if they set a cookie when you click an ads, it's not really lost. Well, it is if a scammer uses a script or something, but if it's just "Click the ads to support the site" or something like that, there's still hope for a future sale.
Of course, the **** ROI is all frelled up because of certain scammers, there's no doubt about it, but there's nothing to do except manually approving each ad placement.
And Google / Yahoo will never doo that. Imagine all the costs involved 
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