[SaintSal]

Thanks for raising that. I've clarified in the post:

There are marketplaces to buy and sell consumer data orginally started around credit agencies and direct mail companies, then growing with the browser toolbar industry when Internet Explorer was big - now they're filled with more information than ever before.

http://www.propublica.org/article/everything-we-know-about-w...

When I worked for a direct marketing arm of the agenccy JWT, we had a bunch of "list augementation" services for our clients' customer lists. Back then, they were used to derive and clean contact information, and glean insights into people's psychology via course methods like correlations to their postal code. (This was surprisingly accurate in Canada, but didn't work as well with US ZIP codes.)

That said, I'd love to hear from a modern insider too. I've just extrapolated.