Ask HN: Recruiting firm promising paycheck

I'm not going to get into too many specifics here, but a recruiting firm put me through 2 technical interviews, located in a major metropolitan area, and later decided they were going to guarantee a paycheck even if we don't obtain a contract w/in 'X'# of weeks. In return I'm expected to provide 100% exclusivity. I've never come across this sort of thing. Is this common in big cities like NYC, SF, Chicago? EDIT: I have not made a decision yet.