Druff
I think you made the correct decision, Moneymaker doesn't have to pay, but you reasoning was wrong ("fictious person")....
The basic rule in law is that fraudlent contracts are unenforceable by the courts or legal system. So while there was a contract (sportsbet) it was a fraudlent one...Moneymaker was induced into the contract by Jason's fraud of saying he was an agent with full authority to take bets for a bookie able to payoff bets taken from Moneymaker. Indeed, there is an implied warrenty in any contract of a bookmaker that the bookmaker can cover all bets he loses.
I understand the legal definetion of a fraud is a knowingly made misrepresentation of a material fact done with intention to deceive, the deception was relied upon and loss was caused. That seems to fit here: the actions of Jason (misrepresentation, intent to mislead, knowlingly made) plus a loss to Moneymaker (that is him being in a contract he can not profit from). But it would be up to a trial court to find decide what is the truth here and a judge to apply the law to the facts.
Also, i believe Nevada is the only state that holds gambling debt are enforceable, no other state allows one to use the courts to enforce these types of contracts.
To wrap it up neatly, Moneymaker should say to Jason what our all hebrew friends say: "Aw, so sue me"