Shoemoney posts that Google claim to be using conversion data to identify arbitragers:
“Kim explained that in many cases they are using Adwords conversion data to tell what MFA sites were actaully converting for advertisers. She said using this data helps them easily identify arbitragers. I think everyone in the room was a little shocked when Kim revealed that Google Adsense was using advertisers Adwords conversion data to actually keep track of what Adsense accounts were converting to sales and which ones were not”.
It’s conceivable that all Adsense payouts may work this way. If a Adsense listing provides a “return” (however that is measured – could be a visit of x seconds) to the advertiser, then the publisher gets paid a higher amount for placement than a page that just sends (back)clicks.
Of course, this depends on what Google considers a return and what information Google has available.