Yes, Google says they invalidate clicks with some unknown algorithm. Trust us, we take care of the fake clicks they say. As someone who has been working as an Ad Words advertiser for the last 15 years, I can tell you that very few clicks become invalidated on this system. Think about it, do you really think the shareholders of Google want to let a major source of revenue go? No.
If Google really wanted to be transparent, they would show you the IP addresses that have clicked on your ads, and limit the “pay” part of the clicks after 1. I see at least 3 clicks go through from the unsophisticated clickers (back button, click on you, back button) and more from the more advanced ones. If you advertise on google, call them. Ask them to tell you the IP clicks that they have charged you for. They won’t; and the reason is – you’d be shocked at how much waste happens from ad spend. They like it that way, it makes them more money. Ad Click Filter helps you limit this.