As much as they're interviewing you, you're interviewing them as well. If you're a smart guy, you hopefully have enough prospects that if you don't want to work with pedantic nitwits, you don't have to.
I was interviewing them as well, but I was 4 months unemployed with a disabled wife that couldn't work but whose disability claim was in limbo. I might have actually taken the job had I been offered one, sadly.
Fortunately, all's well that ends well. An old headhunter I'd used in the past tossed my info along (for FREE!) to my current boss. After talking to me on the phone, he gave me the old "We don't have a position open, but I'll call you if something opens up" line. I wrote it off, but he worked to get a position opened up for me and I'm genuinely doing what I love to do for a living these days. It involves Information Security, physical security/surveillance and general-purpose IT work (Sysadmin, programming and networking). I'm basically in geek heaven. It's also 6 miles from home, giving me the perfect excuse to ride my bike to work every day, rain or shine.
No. In my case, I worked for the headhunter as a consultant to a company that eventually hired me. The agency takes a percentage of the first year's salary in many of these situations. That said, I had really good luck with this agency and the recruiter himself personally. Many are scum-bags. If you find a good one, keep 'em on speed dial. You never know when you or a friend will want some help finding work.
