Help needed; how to make a game with more then 2 players fair?

So like I said in a previous thread I'm thinking of some new games to play or new ways to gamble
But I've run into a problem

When you have a 1vs1 game there isn't a way to cheat in numbers (yes you can cheat by many different ways but not in numbers)
When it's a 3 player game FFA You always have the possibility that someone plays with 2 accounts or such vs the other one.

You can overcome this I thought with a anonymous matching system based on your preferences. But the problem here is that if you have low numbers of players, and I will probably in the beginning, then it would still be easy to "land" in the game you want to. Thus enabling cheating again.

Are there any other ways to overcome this issue?? To have a 3/4/5/6/7/8/9 FFA without enabling cheating?