How has that problem been resolved in offline (print/TV/display) advertising be solved, and could those solutions be reused for the web?
It seems like the free-for-all with regards to personal data and decriminalisation of spyware has led the online ads market into a near-optimal situation with regards to targeting & fraud detection, but 1) is it a trade-off people are willing to accept (the GDPR being enacted suggests not) and 2) can there be alternatives that give both sides what they want?