Been wondering this for a little while now.
Take this example:-
You have your site advertised on a site and your paying per click.
They say you have had 15 clicks in one day but your apache logs show 1 - could this be search engines following the links as they are links on their site which then send you off to mine after processing and I would presume the SE would make a note of the link out once it is passed it and not follow it but by that time their system has charged you as it has seen a click on their internal link to my site?
In the "view source" of the site in question the links do not have rel nofollow on them.
Does anyone have any knowledge of this kind of thing as I have a feeling we have been charged for a lot of of clicks that we have not had delivered.