[rtpg]

>Trusting Google to not sell you out is a level of trust established... how?

It's trust from potential destruction. If Google was obviously using your email contents to sell you out, then people would stop using the service. It's like how people don't want to give out their email address to certain organisations out of fear of spam and phishing.

Google can't exist without that trust, so they're incentivised to act in a trustworthy manner.