Maybe it's common sense, but the quest Total Dominance (Win 7 games in any mode) actually works in ANY mode, including Real ID and Battle Tag matches. So, if you happen to have it, simply join a friend and ask him to surrender 7 times against you. It will take no more than 2 minutes and you will get 100 gold. I think it's a clever use of game mechanics and not an exploit. You can also use a second Battle.Net account that you own, but that may be against the rules.