But if you can get actually get this data, maybe try to do this on yourself and write a blogpost about it. I highly doubt you’ll be able to.
That said, I agree with the rest of your point - you’re not going to go to a developer and offer them $100 for this data on a person (and if you could, you’d still need to tell them which person, which if you could do you could just get the data yourself)
https://www.npr.org/sections/alltechconsidered/2014/09/15/34...
It’s crazy to me that people are being so skeptical of the idea. A lot of people share their logins freely with their spouses. I have never done it nor would I condone it, but it would be trivial for me to install spyware on the devices of many people I know, because they rightfully trust me. Not only do I know some of their device passwords¹, being “the computer guy” I could just outright ask for it or get them to input it anywhere while fixing some issue they have.
¹ And many more I have forgotten, because I make it a point to not record them, even mentally.