In addition to ad spots on SERPs, the major advertising networks allow for contextual ads to be placed on the properties of 3rd-parties with whom they have partnered. These publishers sign up to host ads on behalf of the network. In return, they receive a portion of the ad revenue that the network generates, which can be anywhere from 50% to over 80% of the gross revenue paid by advertisers. These properties are often referred to as a content network and the ads on them as contextual ads due to the fact that the ad spots are associated with keywords based on the context of the page on which they are found. In general, ads on content networks have a much lower CTR and CR than ads found on SERPs and consequently are less highly valued. Content network properties can include websites, newsletters, and e-mails.
Advertisers pay for each click they receive, with the actual amount paid based on the amount bid. It is common practice amongst auction hosts to charge a winning bidder just slightly more (e.g. one penny) than the next highest bidder or the actual amount bid, whichever is lower. This avoids situations where bidders are constantly adjusting their bids by very small amounts to see if they can still win the auction while paying just a little bit less per click.
To maximize success and achieve scale, automated bid management systems can be deployed. These systems can be used directly by the advertiser, though they are more commonly used by advertising agencies that offer PPC bid management as a service. These tools generally allow for bid management at scale, with thousands or even millions of PPC bids controlled by a highly automated system. The system generally sets each bid based on the goal that has been set for it, such as maximize profit, maximize traffic at breakeven, and so forth. The system is usually tied into the advertiser's website and fed the results of each click, which then allows it to set bids. The effectiveness of these systems is directly related to the quality and quantity of the performance data that they have to work with - low-traffic ads can lead to a scarcity of data problem that renders many bid management tools useless at worst, or inefficient at best.