If I apply for a job at Google, how can I make sure they won't use sensitive information in my Google account to screen me?

I, too, am not speaking for Google, just as an individual. There are three reasons you can be sure: 1. Technical reasons. Google employees can't just randomly access private user data. The question details say "since it's stored at Google," but it's not like there is one big hard drive that holds all the data that Google processes. User data is encrypted and can only be accessed by specific programs running with specific permissions. What prevents me from "looking up [your] name" is that I simply can't do it. 2. Legal reasons. I am not a lawyer, but it seems to me that such access would violate Google's Privacy Policy. Google has to answer to various governments around the world for its behavior. 3. Common sense/ethics/public relations reasons. The question asks, "how can I make sure"? Perhaps, on a philosophical level, you can't really be sure of this, any more than you can really be sure that Katy Perry will not be the starting quarterback for the Denver Broncos next season. But for this to occur, you'd have to believe that Google recruiters and hiring committee members were choosing to violate Google's Privacy Policy, risking employment consequences personally or legal and PR consequences for Google. (Look at all the damage done by the revelations about the NSA attacking Google's private fiber-optic cables connecting Google's data centers!) If you do get hired, then you'll be able to see from the inside just how seriously we take user data. No Google employee I know would ever dream of even suggesting doing anything like that, even if we did have the technical means to do so, which we don't (see #1). If any Google employee did do this, it would look badly for Google. If it were widespread enough, many Google employees would probably resign -- I get job inquiries in my email every day, so it's not like I couldn't go somewhere else. Google employees proudly fight to protect our users' data from unlawful access, even when that involves challenging governments.

Screeners don't have an infinite amount of time to consider each candidate.  That is one of your best protections, which insures that most screeners won't cyberstalk you, spend hours reviewing your open source contributions, or make any attempt to look into your private data.