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If you're visitors are indeed highly targeted and are willing to open their wallets, you will still need to provide the potential advertisers with expected impressions, expected CTR. This is essential so they can predict their spend on you're site.
Anyone looking to post ads on your site with any knowledge of PPC is going to be able to quickly research (Overture, AdWords) what they are paying elsewhere for PPC...and if your traffic is highly targeted and highly motivated...this should more so be the case....