An ad server system takes into consideration information about a user who clicks on an ad in determining whether to charge the advertiser for the click event, and/or in determining an amount to charge the advertiser. In one embodiment, unless the user is recognized, the advertiser is not charged for the ad selection event. Thus, advertisers do not have to pay the ad placement provider when the users who click on their ads are not recognized. If the user is recognized, the ad server system may determine whether and/or how much to charge the advertiser based on information about the recognized user. This information may include, for example, whether the user has set up an account, whether a valid credit card is on file for the user, and/or other types of user information that can be used to hold fraudulent users accountable for their actions.