> Even the GDPR gives us enormous leeway to do literally this, but it requires participating in tracking networks that have what amounts to a total knowledge of purchases and browsing you do on the internet. That's the only way they work at all.

That data sounds like it would be very valuable.

But I think if I sell widgets and a prospective customer browsers my site, telling my competitors (via a data broker) that customer is in the market for widgets is not a smart move.

How do such tracking networks get the cooperation of retailers, when it’s against the retailers interests to have their customers tracked?