Amazon.com's search engine, A9, was an utter flop. But now it has entered the profitable side of the search engine business with Amazon Product Ads. The new ads direct customers to third-party sites on a cost-per-click basis. Which is how Google makes all its money, too. Except that Amazon's audience is almost entirely shoppers, while Google has a large cohort searching for Linux drivers. Here's Amazon's product pitch, from an email it blasted out to potential advertisers.

Product Ads is an advertising program designed to give customers seamless access to products available on web sites external to amazon.com. As a seller, you simply upload your catalog and set your cost-per-click bids. We will then display highly targeted ads for your items on select amazon.com product and search pages. Customers can click over to your web site and purchase the product directly from you. Product Ads uses a cost-per-click model, and there are no monthly fees. You only pay for clicks generated by your ads. You can manage how much you spend by setting a daily budget.