No, that would be a massive get-rich-quick style return the way I wrote that. Pennies below a dollar, per annum, in order to get a dollar back as the beneficiary, on average.

It would be tiny fractions of a penny per dollar if you just look at the individual action that causes a purchase, but either it's the accumulated effect of a lot of actions over time, or it's a gamble that doesn't work the vast majority of the time, so you're back to the standard ROI everything has.

It's not just marked ads, by the way. A lot of the stuff that happens with that data is invisible, although I can't say how much exactly.