If someone can explain to me why Amazon and Google haven't figured out a way to integrate GoogleAds and MarketPlace, please do! It could be so simple:
The customer pays Google not for clicks, but for actual successful sales resulting from clicks. Reciprocally, Google could automatically adjust its advertising so that customers' ads appear on the page for the search results that generate the most revenue for the customer. Finally, Google could reward customers whose clicks result in revenue more often by ranking them at the top of the ads page. I haven't recently followed up the GoogleAd bombs story (you make a bot to click on competitors' ads to relieve them of their money) and whether Google has found a solution for this, but this is a solution that works because you pay per sale, not per click. Hire me? :)
Update 13/06/2006: Well, look what they did. I should stop posting.
Update 30/07/2006: As a sidenote, Froogle already provides seller ratings for some sellers.