For the split or steal game (with the golden balls), here is what I what do.
I would not open either ball, and I would tell the other contestant to pick one at random. Then, he MUST choose split for his own ball if he wants any chance of winning money. If my ball happened to say "steal" after opening, then I would split what I won with him.
I think this would guarantee both of us winning unless he was willing to take the chance of winning nothing.