If someone could give some more information, I'm very interested in this. I always assumed this was taking place, but I'd love to hear from someone involved or with knowledge of that industry. Who do ISPs sell it to? What type of money is involved?
You can buy advertising profiles (or access to them) but this not really useful for things that are not directly advertising as it is super aggregated. In general the ISP data is less valuable since so much of the web has moved to using SSL.
I don't know much about how this has changed over the last couple of years but maybe someone else can chime in.