It depends. In my BCA league you must watch the table. If your opponent fouls, it is up to you to spot it. If you don't he has no obligation to tell you anything. I haven't played anything but BCA league, and that is the rule. Everyone is aware of this rule, so people watch their matches very closely.
With that said, if I was playing in more casual league, or for that matter playing an individual one on one, I would be honest, and hand him the ball.
With that said, if I was playing in more casual league, or for that matter playing an individual one on one, I would be honest, and hand him the ball.