Google will not credit all clicks. If its algo thinks clicks are dubious in nature (due to a variety of reasons), they will discard those clicks. Please remember that there is an adword advertiser who is paying for all those clicks and they don't like useless clicks.
In google adsense there is option in every adsense unit settings under More Options. You can choose public service ads, fill with solid color, show non-google ads. Choose one and save settings.
Friend i get 15 clicks but earning is 30 cent tomorrow i get 12 clicks but earning is 25 cent Please help me . . . . .
Google will also not pay for "bounce" clicks. If someone clicks by mistake, then hits the back button right away, or closes the browser.
either they are PSAs or clicked from same ISP as urs [google doesnt allow clicks from same subnet.] -- Bank on Me
They must be very low paying ads or its related to click fraud. I was geeting the same thing before and I know how you feel.
Invalid Clicks! the clicks you receiving on behalf in your sites are illegal. Check & Analyse your site traffic source because in several hosting spammers tend to do it
It is very common. Those are invalid clicks and I believe most of adsense accounts have experienced this.