A while ago, the madvertise SDK had a bug which resulted in ads not being scaled. This resulted in very small ads that were clicked by accident almost all the time. After a while, this bug was fixed. When looking at the conversion rate for my house ads, it was totally obvious that the non-accidental clicks resulted in a respectable conversion while the accidental clicks had almost no positive effect. I think the google AdSense for mobile do a good jobs here because the user has to click them twice before anything happens.