Two games in a row, I had an "unranked" player that clearly had skill above our level and got many multi-kills in the first few rounds then suddenly go quiet for the rest of the game after realizing that the rest of the team might win. By "go quiet", I mean 0 kills for the rest of the game. That player was evidently trying to lower his own rank to smurf.

I'd recommend dodging them, you might get a smurf, someone at the right level, or someone trying to lower their rank to smurf harder. It's just not worth it.