What's the inside behind the scenes story on "Undercover Boss"?

I am curious about several things that go on in this show. How do the undercover bosses end up with the people that have the major personal issues? Are employees researched before hand? Or is it just luck of the draw-everyone has a story to tell type scenario? And do only the four or five employees filmed get a special perk or does that happen to several employees? Any other info?