netmeg - 9:52 pm on Jun 5, 2013 (gmt 0)
No you can't tell for sure, and that's on purpose. Google doesn't want you to be able to cherry pick ads like that.
Google has always claimed they enter the auction like all the other advertisers, and their ad comes up only if it's the best available at the time.
If you are seeing a lot of Google ads, then maybe your audience is tech oriented, or maybe your topic doesn't have a lot of other advertisers bidding for your placements.