Google gets paid by placing ads. While deciding what ad to place, they broadcast your profile to the highest bidder. This process is repeated every time you visit a page with ads. I totally simplified it by saying it like that, but that's essentially what happens with people's profile these days.
Google sells access to your eyeballs. This is very different from "selling your information", which is what a lot of other companies actually do, including many in the off-line world. For example, it's very easy to buy a mailing list. Years ago I used to buy targeted mailing lists from various magazines.
Some people just need to make Google out to be the bad guy. Apple fans used to hate Microsoft. Now they hate Google. They always need someone to hate. And just like they (myself included) spun FUD about Microsoft back in the day, today they do the same with Google. Truth is, Google isn't nearly the worst offender. As I mentioned in another post, the Weather Channel is really shady and is being sued over their shady practices. There are many apps and services on the App Store today that make what Google does pale in comparison.
Selling your information would be the stupidest thing Google could do. That's their biggest asset. I'm not a huge fan of what they do, but I'm also tired of the ignorant, ill-informed fanboy narrative that Google is broadcasting your private information to the world. They are not. They are gathering information and building a profile about you. The more information they gather, the more valuable the profile becomes. They use that profile to feed you ads. They never sell that profile information to third parties.