I realized that a lot of clicks from Yahoo aren't "legit." A lot of them are fraud clicks. How do they compare to Microsoft and Google for fraud clicks? Thanks!
Yahoo is a lot dumber when it comes to detecting fraud. Is that the question you are looking to answer?
Believe me yahoo is 3 tiems worse then google. You can prevent google ppc by using bracketed keywords and only do google based ads no content network.
If yahoo develops a better click fraud detection system they may be able to give google a bit more competition.