Physician recruiters are paid one of three ways:
1. Retainer -- They are paid regardless of whether the position is filled or not, with another payment when the position is filled. This is usually a large national chain -- Cejka, Jackson & Coker, Merritt/Hawkins etc. Large clients (i.e. univeristy programs or other large health care systems) hire them. They screen applicants carefully, and send a small number of highly qualified, well matched candidates for interviews.
2. Contingency -- the position is given to a recruiter, they get a fee if the position is filled. Key to understanding this is that Physician recruiters do not "share" fees like real estate agents. A PR will only show you "their" listings, not anyone elses. They are likely to send your CV to all of their contacts, hoping for a nibble. They really don't care if it fits your needs at all (not quite true, but close).
3. IN House -- some big systems have salaried, in house recuiters, very similar to #1.
So:
A. Going with a large national firm is a reasonable choice, but you're only likely to find jobs listed at big places.
B. No matter what you do, do not become "married" to a physician recruiter. You must use multiple recruiters, as they will each have different listings.
C. Assume all PR's are "used car salesmen" until proven otherwise. Do not give them a copy of your CV until you have heard of a job in which you are interested, and preferably not until after you have spoken to someone offering the position (although this is often impossible).. Make sure any PR's you are using know 1) how to contact you (i.e. do you want to be paged), 2) What exactly you are interested in and not, and 3) that you will fire them if they misbehave, by sending your CV anywhere you did not expressly approve.