I have just started two campaigns with adwords and I realize that click fraud is a part of this. How can I know if this is happening?
If you are still not convinced then stop advertising on Google partner sites or you can also place your ads on select partner sites.
For an e-commerce site, high clicks and very low conversion rates can signal such, along with a bunch of other aspects. I hope this helps a little. -Aaron
Google does a very good job of catching fraudulent clicks, that doesn't mean they will catch them immediately. I've had refunds come in the month after for fraudulent clicks they found after looking at the prior month.
www.adwatcher.com and www.clicksentinel.com are two of the programs I've heard deal with this situation successfuly. Check them on google, too.
Google does a very good job monitor fradualant clicks, so I wouldn't worry about it. I have been advertising with Google for some time and have not had any issues.