Paybuyer will always tell you how much advertisers are paying for your attention, unlike Google and other ad media.

Google says:

“Google’s mission is to organize the world’s information and make it universally accessible and useful.”

Yet, Google won't show you how much advertisers are paying for your clicks. Bing, Yahoo, and other search engines hide this information, too.

This secrecy has worked: most users are clueless. We asked a couple of hundred people to guess how much Google collects for a click under "auto insurance." Approximately, 25% said 5 cents or less, 66% said 25 cents or less, and over 90% were surprised to learn it's ~$45., Oct. 2000.
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In the beginning, click prices were shown.

Auction-based, pay-per-click search advertising, used by Google, Bing, and Yahoo, was developed by a company called in 1998, which started out displaying prices with each link:

"So [Bill Gross] launched a company with exclusively paid search. He said it was better than the Yellow Pages because he would provide pricing transparency. Users would know exactly how much was paid for each click." - Both Sides of the Table became Overture and was sold to Yahoo in 2003.