[gadders]

Normally, you (the contractor) is quoted a rate of £xxx/day, and the agency's % is on top of that and normally unknown to you.

You typically sign a contract with the recruitment agency, who has a back-to-back contract with the end employer. The contract basically just says you will be working at employer X for Z months.

There will be other legalise about intellectual property, confidentiality etc but that is the gist of it.

The flow of a job opening is normally that a hiring company will send the vacancy details to a shortlist of preferred recruitment agencies. These agencies will then submit CVs of candidates on their books back to the hiring company. Then the interview process etc starts.

To answer your specific question: agents can represent multiple candidates (a database of thousands) and a wise contractor would not rely on just one agency (my CV for example is probably with ~10 or so).

This is specific to the UK market - other markets may vary.

[gadders]

Also, recruitment agents are "employed" by the candidate and they will often say during negotiations "that the more you get paid, the more they make".

However, this is subject to the same issue that Freakonomics highlights vis Real Estate agents and house sales.