I look at how many page views and clicks i have. If rate is very high i would watch site to see if i have a problem.
Depends on what kind of ad it is.. If you redirect all clicks to an script on your server, you can check if the users have been clicking before. If he has, he will be sent to the site without an affiliate code, and if he hasn't, he will be sent with the affiliate code!
I heard this was fixed when they recently upgraded the software (adlogger) I had weird clicks, 2 page impressions and 5 clicks, that doesn't make much sense to me.