Thanks for the response Woodrow. I understand that LeeD is wrong about the rule, but I'm not convinced that it's such a straightforward call for the player who is chasing the ball.
The fact that it's happened multiple times with opponents who don't strike me as dishonest in their other calls makes me wonder. If they had anything near as clear of a view of the second bounce as I did they were definitely cheating and I don't think that was the case.
For what it's worth, none of these calls were at the baseline-- they were all around the service line. My impression (could be wrong) is that double-bounce calls at or behind the baseline are relatively rare, and that when a controversy occurs it's usually with a player charging forward to get a short ball.