When I was working in the oil & gas business (commercial world) I was the liaison with our HR department because they didn't have anyone who could evaluate programmer quality. We used different recruitment teams at different times and all I could say was, they were a mixed bag.
More specifically, some companies sent us folks who worked out great - but one company sent us rejects, misfits, and outright nincompoops. One of their candidates wanted to get into real-time programming and his qualifications were that he had a programmable hand-held calculator. Another candidate had a Master's degree in Pharmacology from the University of the Ryukyus (Okinawa group) with a thesis on psychoactive herbs of the Pacific Islands. His letter included a typical "hippie" salutation. The guy's relocation fees would have been horrific given the distance.
Like any other business, head-hunter recruitment firms depend on the management and employees. When looking for ditch-diggers, not too hard to figure out. When looking for higher-tech, ... they send you ditch diggers. Yeah, I know sometimes we talk about "working down in the trenches" - but we don't meant it literally.