If you are that concerned with people and odds posted, either only give certain members Bookie access, or an Admin will have to check all outcomes before posted.
You run a forum, you should know you are not going to please every single member with every single decision.
You could also get StockTrader, and have your members invest.
Currently, I see Usergroup Styling options [ bold, italic or underline username] at our site, costing $50,000 each. Members still start out with 5k. They still earn from posting. If they want the 50k that bad, they can either post and reply more, or use Sportsbook. Once they upgrade, they have access to StockTrader as well. Do other things to get currency entered. Run a Signature of the Week type thing, Post of the Week, Rant of the Week, Pic of the Week, Member of the Month... offer prizes of how many points you want. There are tons of ways to use all of this, as well as using Sportsbook without someone gaining too much.