On my Google AdSense payment history: Jan 28 2013: Invalid Traffic - AdSense for Content
They reduced my monthly payment with about 1% of the total sum. No explanations, no nothing. They're just claiming that I'm not following the mutual agreement made about AdSense usage policy and provide no proof of that. Quite literally they're saying is that I'm abusing the system to gain extra payments out of Google and if not abusing the system, I'm a liar because I don't admit doing that. Nice!
There is a discussion thread Help to identify Invalid Traffic Source in the Google AdSense in English support forums. Lot of people having this issue since December 2012, and no possibility of tracking who clicked what to cause the alleged invalid clicks.
This is not about the 1% of lost revenue, it's about me being called a liar and not introducing any kind of evidence what I did. The AdSense payments fluctuate a lot anyway, they somewhat correlate with visitor flow, but sometimes Google issues more expensive ads which yield more cost-per-click. Then again they issue cheaper ads with lower CPC. Since they get to control who gets what, in the end it is a zero-sum-game and on a monthly payment differences equal out resulting something that correlates the site visitor flow. But this 100% control is not enough for them, they don't want to pay out what they're agreed to do and get 101% of control.
It is needless to say this, but I'm doing it anyway: This sucks like a Kirby vacuum cleaner scam!