How do employers get to the stuff you've posted on Facebook?

I know plenty of people who applied for jobs with the state (police, social work, etc) and deleted their facebook pages until they were hired (or not), because they didn’t want anyone getting to their information.

I’ve heard from a lot of people that employers will sometimes look at your facebook page and review the content before making a decision about hiring you.

My question is, if you have all of your content set to be viewed only by confirmed friends, how do they get to this information?