Because an old habit, I use a web tracking service that has nothing to do with Google. And I use Google Analytics and Google AdSense as well. Lately I have noticed that results with Analytics and AdSense are not going hand in hand, but yesterday my eyes opened a lot when I looked the "Exit link report" of the third party tracking service and it showed me that my visitors had clicked AdSense ads in one of my sideshow sites pages but AdSense didn't report these clicks. When I looked the situation via Analytics Adsense report, it showed me exactly the same amount of clicks and even the money earned – or atleast I should earn. This site is a little sideshow and it's purpose is to collect the traffic with less common keywords. It has about 20 - 50 visitors per day and 100 - 200 page views. It's not a money maker, but I'm showing the AdSense ads with it and sometimes I can see some revenue coming. So I'm not talking about big loss of revenue here – something close to $1,50. But still it's very strange to see reports that shows you some clicks and the AdSense reports you zero clicks. Question is that can you trust AdSense reports? Sure, you have to, but if the same thing happens to every AdSense publisher in the world just once, Google will get millions and billions of profit straight out of our pockets.
I have this issues all the time, especially that I use Statcounter for tracking and I found in the exit link everyday something like 10 clicks but in the reports I hardly find 5 to 6 clicks. But we still have to trust these reports and say maybe there were invalid clicks or something like that!