For example in the Automotive industry a mail piece with a tracked phone number is used and that is cross referenced with Dealer sales data. The pieces are mailed to targeted lists of people qualified by credit score, postal code and recent purchase of vehicle make. Should the site be accessed via a personalized URL the user now appears through a variety of methods, same if they come from FB they’re claimed through offline conversions where sales data is compared to audiences. Using this readily sold and available data it’s easy to calculate spend and determine response. Even with single digit response (not uncommon for email) industries thrive.