My GF is temping at the moment. She quite likes it at the current place, they say they like her and want to keep her and there are three permanent roles coming up.
If they openly advertise the roles and interview applicants then the agency will get nothing (as a right) but of course this has the risk that a better applicant will apply and get the job.
Otherwise the agency will probably have covered the 'introduction fee' as part of their terms and conditions as they have a business to run.
This of course leads to the moral issue of those employers which go through the motion of advertise/shortlist/interview when there is already a choosen one. It happens and should not be allowed preferrably with a criminal penalty attached to stop repeated offenders.