Purchase data has been around for years. Marketers want to know if their ad dollars worked. “How did you hear about us?” provides scant and mostly unusable data

Purchase data has been around for years. Marketers want to know if their ad dollars worked. “How did you hear about us?” provides scant and mostly unusable data. By matching purchase data with ad campaign data there can be more quantitative evaluation of an ad campaign’s performance. Additionally I imagine this data is available for marketers to target buyers of Product X with Accessory Y. Finally, marketers may use purchase data to build suppression lists; ie. Stop retargeting people that already purchased Product X. I don’t know if this happens very often in practice. It’s very hard to do well in general, and generally cheaper to spam people than buy data to shrink your list. None of this is well-disclosed to consumers, not one bit of it is right. It just is, and it has been for going on for 8+ years.