You just need a few friends that will put pressure on the kids to pay if they don't. You don't need some vanilla ice tactic like what happened to goldy, just some guys that run harassment until the debt is settled. If the amount of credit you are extending to your "friend" is worth physically harming them then I would say keep them on an amount you could handle if/when you get stiffed. Personally I would not book bets from my friends other than friendly side wagers but I certainly understand why guys do. Great way to make money for sure.
Edit sorry Reigle I have no worthwhile help on your original post.