I doubt think they do many hits these days (In America) In reality you need a damn air tight science suit not to leave behind any DNA, and unless you do it alone, your gonna get ratted on either 10 months or ten years it will come back to bite you.

BUT the hits that they do take on, I would suppose it would be a reliable guy doing the shooting and maybe an associate they want to have made taking part so technically he will have "made his bones".