The incentive to show post-purchase ads is: 1. people didn't like nth purchase so they're looking for a substitute. 2. reinforce purchase behaviors / reduce buy

The incentive to show post-purchase ads is: 1. people didn't like nth purchase so they're looking for a substitute. 2. reinforce purchase behaviors / reduce buyer's remorse. Ads work at human psychology; they're not fully logical. Though I'm sure there's inefficiency in marketing but if post-purchase ads weren't ROI positive, I doubt the market would be paying for them.