I've strictly used firms that are paid a percentage of my signed salary by the company upon hiring me. This heavily aligns incentives in much the way agents are aligned with athletes so that I maximize my compensation when I'm looking for work. Singlesprout comes to mind here. I'm still responsible for swatting down roles I don't like but when I see one I like I know they'll go to bat to maximize their own earnings.

Though I ultimately didn't take their offer because I was able to play it against a local company for a matching salary and bonus to avoid a move it was a good experience working with them and only mildly painful to break it to them that I would be taking another offer.