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It's something thats been done in other games, but some sort of penalty, have the game keep track of every time you either quit a match, or your the first one to quit a match and then have a delay based on the number of times you've quit first before you can take another match. This would discourage syncing and probably help a bit, maybe 5 seconds for every 10-30 quits, wich will quickly add up making it a waste of time for those that try to sync or are lookinbg for those 'perfect' teams.

... or at least something like this... i hate leavers XI