Can't speak for Google, but Facebook certainly doesn't sell personal data. Facebook internally uses personal data to show targeted advertisements. Big difference.
Nor does Google. Twitter, however, does. That being said, Twitter is default public and they've been really open about it since day one.
Note: I have no special knowledge of Google, so maybe they do. Given that it would be really dumb to do so and lie about it, I believe that they do not.
It just sells access to use the data, not to know what the data is.
Their proposition is: "Give us $50 and you can target 26 year old iPhone users who go to Stanford and have posted about bratwurst in the past six hours."
You're paying to use the data they've collected about their users.
If they didn't sell access to use personal data, we'd be back to flat banner ads with no retargeting or privacy invading doubleclick social strata pinning.
Note: I have no special knowledge of Google, so maybe they do. Given that it would be really dumb to do so and lie about it, I believe that they do not.