Final answer:
Advertisers who pay only when a visitor takes a specific action like a sale or form submission use CPA or PPA as a performance measure, ensuring budget is spent on interested leads.
Step-by-step explanation:
Advertisers who pay only for a visitor who has expressed an interest in their ads typically use a performance measure known as Cost Per Action (CPA) or Pay Per Action (PPA). This model ensures that the advertiser pays only when a specified action, such as a sale, a form submission, or a click, is completed by a visitor. For example, if an advertiser is promoting a new product, they might set up a CPA campaign where they pay for each completed purchase that originated from their ad, thereby ensuring that their advertising budget is spent on leads that have demonstrated a clear interest in their offer.