That's just one of several reasons why Employment Agencies are not redundant.Agree with all the postings. But I have one query to add. Even within the employment agencies there are categories. Some agency deal mainly in so called blue collar workers or part-timers or contract ppl etc.
There are some so called high-class agency that deal with vice president, director, CEO kinda. This kind are so high class that if a successful deal goes through, the company can feed their employees for at least half a year to one year. Of cuz the recruitment consultant in such high class agency muz dress and speak well.

As to comission for contract, part timers I am not sure but for permanent post, I think it is the a percentage of the starting pay of the successful candidate that goes through. It is say the first 3 months of that candidate? Sometimes agency call the candidate personally to check ard how much they are offered in case they scared the company lie to agency about the pay and pay them lesser.
Exampe Company recruit employee A at $X but they tell the agency who recommend A to them it is at $X - 500 ? So agency scared lose out will secretly called A and check out the rate discreetly

I know cuz I was the employee A a few times.