The idea that Google (or any major tech company!) has ever even considered selling user data is highly damaging to our industry. I don't expect that kind of baseless paranoia on Hacker News.
(in case you are not)
Yes Google sells user to their paying customers -- advertisers. How do you think they make all those billions of dollars / year? Why are they providing you with free Gmail, Maps, and high quality search results? The answer is that they sell you to their customers. If you are in gmail and sent your mom an email telling her what kind of printer cartridges to buy, don't be surprised if you see an ad about printer cartridges. They indirectly sold your data "interested in printer cartridges" to their "real" customer -- the company that makes printer cartridges and is looking for someone to buy them.