What I've noticed personally is that searching/researching for some very specific purchasable term (e.g. Love sac furniture) triggers the targeted advertisting. The thing is, the ad agency does not know whether I've made the purchase or not. Usually, I'll start researching something 1 day to 2-3months before purchasing depending on how large of a purchase it is, so the ads are useful up to the point I use the ad to make the purchase. Unfortunately, after the purchase is done, the ad just becomes irrelevant and annoying.

So there's probably a significant number of people where targeted advertising is able to get the click that leads to the purchase. In reality, it's probably just taking organic traffic that would have purchased anyway and counting it as a targeted advertising win versus an organic purchase.