There are two ways to determine the charges for PPC:
PPC Bidding: In this method, an amount is specified by the advertiser to go for a bid. The advertiser specifies a maximum amount which he is ready to pay for each time a user clicks on ad. This method is also called max CPC. This is the most used type.
Flat rate PPC: As the name specifies, it is a predefined charge for advertising between the advertiser and the publisher. The charges may differ from page to page and content to content.