I would not know how to wager on FR. But let me ask you, what do you see in Faber over Barao? This guy is as good as Aldo in his weight class. Faber is good, but he lack skill in Mui Tai. Faber is good on the ground. Faber is not near as good as Barao in striking. Faber is OK in submission, mostly due to his strength and endurance, but still not as good as Barao. I do not see any weakness in Barao.
As far as wagers, your word is your bond. If you agree to terms just say so and bet is on.