Originally Posted by gmatheis
Actually, they do have an obligation to do so.
13. Player calls own shots out. With the exception of the first serve, a player should call out the player’s own shots if the player clearly sees the ball out regardless of whether requested to do so by an opponent. The prime objective in making calls is accuracy. All players should cooperate to attain this objective.
If they saw it clearly, then sure. But as the other player you have no way of knowing if they saw it clearly out, or just thought it may have been out. If they just thought it may have been out, they of course are under no obligation to call it out. Good luck proving that they saw it clearly when you didn't even see it clearly.