Disclosures and information is the key.
For a start, If you have played with one person in a game, in the next game it should to all players if there are players who have played together in previous games.
As for fake accounts or newbie accounts, that will try to bypass game history...Subterfuge should let ALL players in the game know if people are playing from the same IP or device.
I don't care if you are triplet brothers playing along with your dad, mom and pet donkey in a game of 8.. Go ahead. If they work together or work against each other, that's upto the 6 of them... but atleast the remaining 2 players know that the relationship the other 6 share.
Finally, if someone is gifted more than x% or x number of subs, then it should be made public after the game is over.. and if they are the winning players, a mod should look if there was any pre-game team partnership and ban the accounts.