“The Spinner* is a service that enables you to subconsciously influence a specific person, by controlling the content on the websites he or she usually visits.
The targeted person gets repetitively exposed to hundreds of items which are placed and disguised as editorial content.
–https://www.thespinner.net/
What makes this creepy as all get-out is that when we think of people using this kind of tool to manipulate the people in their lives, we intuitively understand that this is a tool for sociopaths and psychopaths. When you start thinking about this hard enough, what is the difference between The Spinner and using Google and Facebook to do the same thing for a demographic? There isn’t one. We only call it advertising when it is a group since it isn’t personal. I’m kind of taking it personal.
cafebedouin.org 
I thought at first “how would such a web tool accomplish its stated goal?” But then, you pointed that Google and Facebook already do that (i.e., narrowcasting). Difference is that such power is unlikely to be democratized to rando psychopaths. Big Tech wants to keep it for itself.
The thing about sociopaths/psychopaths is that they are happy to share their tools with others, so long as it’s profitable and it doesn’t undermine them. Giving their data to third-parties for cash is their business model. “Services” like this one work so long as most people don’t know about them. Same with selling location data, stalker apps, etc.
Not that I have much exposure to psychopaths (that I know of), but I don’t imagine there’s a lot of sharing of power. Still, I can see the possibility of a total lack of restraint. The big “if” is whether sharing undermines the goose that lays the golden eggs.
As a rough measure, psychopaths are ~1% of the population. So, 1 per every 100 people you know – and maybe a range of 80-120 depending on your social circle. They tend to be in positions of power, which helps when you’re first trying to figure out who the ones are in your life.