I have played golf games since Tiger Woods '99 game and I remember early on they had a feature where it showed a number by their name pregame.
This number is the percentage of the time the person completes the round. so if you complete 9 out of 10 games you would have a 90 percent completion percentage.
so lets say players in the 90's have a green number, 75-90 percent have a yellow number, anywhere below that has a red number cautioning players to avoid the player.
I remember this worked extremely well because players who were below 75 percentile had a real hard time getting a game.
Another idea would be to raise peoples average .1 percent every time they quit a game. Being that people care so much about their averages, this would likely were very well also.
Just my two cents,
AB