Betting against your teamate would kill your team's ranking unless the bets are completely separate from the normal betting system .
so basically , it would take another separate betting system just to bet against your friends.
I think it is ok like we are now, i mean, if a guy want to bet against another they do very often an avatar bet witch is very funny when we see the loser having a ridiculous " i love fedorwin " avatar or when a guy have the dallas cowboy avatar when he is a packers fan !!!