Yes - you might assume 'well, they get a percentage of what I get so our interests are aligned'. Sure, they do, but their downside if they don't place you is that they get a percentage of nothing, whereas their downside if they place you for less than your value is they get a percentage of a lot of money instead of a percentage of a load of money. Also, they are hoping to work with the hiring company again, whereas they will likely never have to speak to you after you're hired, so who are they going to do a favor for?
So no, your interests really aren't aligned, and they will screw candidates on salary negotiation, take the slight hit on commission, and then make it up in volume.
So no, your interests really aren't aligned, and they will screw candidates on salary negotiation, take the slight hit on commission, and then make it up in volume.