stitch29 wrote:One possibility is to link the accounts via Facebook and/or Google+. I know it's not always the most popular thing and it won't solve the problem 100% but it is rarer for people to have multiple Facebook and Google+ accounts.
That won't work. Anyone can make another Facebook/google account in 5 minutes. I'm sure some people will do it, but unless there was some sort of prize involved I doubt most people will go through the effort of having 2 players just to win a game.