[Nightblade]

For me it is rather simple, i only play games with friends, either the ones from real life(tm) or the people i met and befriended with over the internet.

When i play with my friends, we always establish rules in our games.

Until now none ever betrayed anybody, has double crossed anyone in an alliance, unless it was an -agreed by everyone- part of those rules we create for our specific game.

This way everyone has fun.
I believe agreed by every players pre-games rules are the way to go to avoid a game to be unfunny in the end for some players.

Now for the case of playing with people you don't know, if they don't resepct some agreed pre-games rules, they are not worth playing with, just play with someone else.