I guess the effectiveness is related to an individual's overall online habits and interests and I would be quite surprised if it did "not work at all" at scale.

I guess the effectiveness is related to an individual's overall online habits and interests and I would be quite surprised if it did "not work at all" at scale. Besides, if it did not work they would know by now... For example, maybe you do not browse a lot before spending money because you know what you want more or less? I have the habit of clearing my browsing data often, all the tracking options in my Google account are off, and the ads I get seem pretty generic in general, but I sure get ads related to my Google searches if there is something concrete to purchase, like hardware parts.