An ad broker is a middleman between advertisers and publishers. These are individuals or media agencies who make their living by finding and negotiating ad spots for advertisers they represent for a fee or percentage of sales from both advertisers and publishers. Ad networks can be referred to as ad brokers as well.
Second-Price Auction
Basically, a second-price auction means that the highest bidder in an auction pays one cent higher than the second-highest bidder. For example, suppose two advertisers