In your stats you may notice that you have earning with 0 clicks...But depends if you have channels and depends if you have luck to notice that
When I go to google and type "mysite.com" with quotes, I see just one company listed on the paid links on the right. They are a direct local competitor, and I see thier ads freq on my site. I don't know if this means they are paying by impression, but I'm certain they have targeted my site to display their ads.