It makes sense that there's some discovery mechanism - since Google loves to use it to prefer Chrome, GMail, etc when you're in one of their apps. I wish that there were more restrictions though where you only get implicit permission to query from apps that have the same developer ID. Maybe a mutual allowlist that has to be formed, or some sort of privileged intent where you at least have to tell Apple what's going on and that gives them some contractual right to sanction you if you're using it for nefarious purposes instead.
[1] excluding the clipboard copy count, that was novel!
So your partner only needs to have had 1 single app from the list that sells user data to a data aggregator for this to work. They do not need to have installed some special app.
Here's a random Slate article about apps getting your data and selling it to aggregators/brokers, who sell it to third-parties (you, or I, could be one of those third parties).
> How Shady Companies Guess Your Religion, Sexual Orientation, and Mental Health And sell that data to the highest bidder.
https://slate.com/technology/2023/04/data-broker-inference-p...
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.