[ghostpepper]

Not the OP, but I am guessing they are trying to say that the distinction between "you pay facebook and they give you a database full of private data" and "you pay facebook and they give you API access to a database of private data and allow you to query it in myriad ways leading to you creating your own database of highly accurate private data" is not as important a distinction as Facebook would have you believe. Or something along those lines.

[umanwizard]

But Facebook doesn’t let advertisers query their database of private data. I agree that if they did, it would not be very different from selling data, but they don’t.

[sasasassy]

But.. they do, though. You can (and people do) make a very targeted ad, then query what users matched with it, and so on until you've sufficient data for your purposes. Plus you can use their public APIs to then match their ad data with the users public information. Facebook knows this, and does not prevent it (by hiding user identifiers for instance) because it's part of their strategy.

[Voxoff]

Ah now this is sneaky. Is this widespread? Any sources?

[ambicapter]

Here's a guy targeting his roommate[0]. Previous discussion[1].

[0] https://ghostinfluence.com/the-ultimate-retaliation-pranking...

[1] https://news.ycombinator.com/item?id=8330931

[scarejunba]

By making a Custom Audience and then selectively uploading? I think you have to agree to not do this.

The audience size tricks like uploading an audience, then adding one to it and reuploading won’t work. There’s a cardinality fudging thing.