Each advertiser informs the host of the maximum amount they are willing to pay for a given ad (often based on a keyword), usually by using online tools to do so. In the bid-based model, each advertiser places an offer with a maximum amount of money that they are willing to pay for an advertising spot. Over time, social media giants have begun to launch advertising regulations that require advertisers to pay more to show their content to their ideal customers. You place your bid into an ad auction and the highest bidder wins, so you could end up paying less than the bid amount, but never again.
When the PPC is working properly, the fee is trivial, because the visit is worth more than what you pay for it. For ads to appear alongside search engine results (commonly referred to as a search engine results page or SERP), advertisers cannot simply pay more to ensure that their ads appear more prominently than competitor ads.