How Google determine an invalid click?

Most bloggers or website owners depend heavily from Google Adsense to generate income. I stumble across to this video discussing on how Google determine an invalid clicks and showing a tool on how you can determine using analytics.

Some readers also curious to know the alternative of using Google Adsense just in case you got booted. One service that comes in mind is using AdBrite. You can easily learn the management console of AdBrite, as similar approach to place campaign ads to your website.

Though, I prefer to get a direct advertisers to my website than using third party services. One obvious advantage is you cut the middleman, both website and ads customers save more money.