willvr:
The fact of the matter; is you get to know people you trust regardless. And if someone that you do trust, privately, says "Careful - he left me stranded in three games" - you'll listen.
I'm not actually a fan even of that level; but I acknowledge that's human nature. But to turn it from a private thing between friends, into a big public thing, is somewhat scary; and will end up blacklisting people; in effect.
Dumping a game is one thing, that I might listen to. If it was involving more than one game, because there might be reasons for the first 'dump'. I can see getting completely fed up with a whole group full of bickering players and just walking away. Past that I won't even do more than take into consideration what my best friend says. There are a lot of things we agree on in games, but some things that are total deal breakers for him are things I enjoy and vice versa.
Yes, I agree, it would end up as a public blacklist. For things that the whole story wouldn't be known publicly. Even if both sides were to tell their stories you might not get the full idea. All it takes is for one person to blow everything out of proportion and one person to not feel the need to defend him/herself against a bunch of bs claims.
I've run a grand total of one game (still ongoing) here. I was VERY picky about who got into the game, I wanted to make certain that the players could accurately play they type of characters in the game. I turned quite a few potential players down because I didn't feel they could do the job. This upset a few people, a couple even tried to argue with me. Because of this I'm sure there are a few people out there that feel that I'm an unreasonable jerk. My response to any long, vitriolic review of me would be: "I didn't feel they could play the part, my game, my rules." Chances are that wouldn't turn anyone to my side and might actually do the opposite. Thing is, I WOULDN'T FEEL THE NEED TO DEFEND MY ACTIONS AS GM.
The other end of the spectrum is something I saw years ago on another site. One of the site owners manipulated dice rolls. It was blatantly obvious, you can only roll so many natural 20's in a row. When you do it fifteen times, roll an 18, then roll ten more 20's (where I finally gave up counting), it's patently obvious you are cheating. Thing is, not many people seemed to care. To me cheating is an unforgivable sin. Obviously there are people that don't mind playing with a cheater. So who would you listen to? One of a few voices mentioning the cheating (before they were kicked off the board) or the 40-50 other players that seemed to have no issues?
All in all, there are just too many ways any system would turn people away from good GMs and not turn people away from bad ones. Ditched games can somewhat be seen just by looking at how many games a GM runs. If the person has started a game a month that only lasts a few hundred posts that might be a sign that any new game won't last. Past that, things fall into objectivity and various likes/dislikes.