The problem with any platform like Facebook (though Facebook happens to be have the richest seam of user data, at scale and across devices) is that the segment

The problem with any platform like Facebook (though Facebook happens to be have the richest seam of user data, at scale and across devices) is that the segment with the highest clickthrough rate will inevitably be one which draws on shady factors. It will be the segment deliberately concocted to find that most vulnerable / subsceptible to buy. If you're looking to ship garbage self help books, you're going to target people who like garbage self help book writers. Rinse and repeat for preppers etc. To prevent this you essentially either have to ask marketers to hobble their own search terms even when they know there is likely a higher CTR out there (like payday loan companies willingly deciding not to advertise on daytime TV), or asking Facebook to hobble its own platform. Until there is some kind of regulation or FTC pushback I can't see the situation improving.