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How does G know if an advertiser puts the conversion tracking code on the page that they really want a surfer to go to? They could put the code on some random page that most surfers don't go to, that way G thinks that the visitor is a poor lead and discounts the adsense referal. Sorry if this has been discussed before, but I haven't been able to find the thread.
Google don't use conversion tracking alone to determine smart pricing. In part because the majority of advertisers don't actually use it at all, but also because Google uses all sorts of data models, including general conversion data for that ad, they type of site, the page content. In fact, they may as well ignore conversion tracking entirely!