Heh... You sound like you have the same attitude most of my preferred staffing agencies have. Most of them, sadly, don't have this attitude. (For example, I will deal with Oxford International, but they're last option for talking to on things... There's a reason for that, which includes excessively low-balling me on past jobs, offering me just any old gig that they think I might be able to fill, never mind that while I'm skilled in Windows development, I flatly DON'T want to do that if I can... And they're just one of dozens I give last chance to or won't at-all talk to/with.)
The agency is supposed to do what you're saying. More often than not, unfortunately, they do what people are posting to on /. on this subject today.