> It's the same in online marketing, you often target people who are searching for say a pair of shoes.
FYI - you're not clearly delineating between capturing intent, prospecting, and branding. Worse, your using intent capture as a catch-all for all advertising. That's not how it works.
> Pizzerias do not attract more customers by giving coupons to people already planning to order a quattro stagioni five minutes from now."
The alternative is that the Pizzeria does zero promotion and those who are interested in "ordering a quattro stagioni five minutes from now" end up going to somewhere that does.
Ads, on Google specifically, is a zero sum game with an auction based fee structure which mostly is about capturing potential customers' intent to buy. This is the true "evil" of Google, as you basically are forced to pay a tax on all online intentions to purchase via a search from Google (it's also why Google is so scared of Amazon...hence, Google Shopping)
> and that it's hard to know ROI, because true advertising effects are tiny if you measure them in an experimen
It's impossible to know equivocally why a person makes a purchase, digital, traditional, or otherwise. Theres a lot of research on this topic but until its conclusive, we'll never have a "true" ROI.