Wait, if they get 20k per candidate hired, and the turnover is 90 days, what kind of schlock does go back to them? And what kind does not sure them when its obv

Wait, if they get 20k per candidate hired, and the turnover is 90 days, what kind of schlock does go back to them? And what kind does not sure them when its obvious the candidate did not have any of the advertised qualifications?