If you don't think you can trust the other participant, you could do the following: Point at one of the other's balls. Say "I will choose steal unless you pick

If you don't think you can trust the other participant, you could do the following: Point at one of the other's balls. Say "I will choose steal unless you pick that one. If you do pick that one, you may choose the ball I'll pick." Unfortunately, your expected value is only 37.5% with this strategy, not 50%. You can still do better if you trust each other.