Well, its not allowed in duels for the ladder. I think anyone caught doing it in ladder duels should be removed. Its not always easy to get a 3rd party to watch. I'm talking in general, I'm positive it wasn't an issue in any of the duels I had, and at this point, wouldn't much matter anyway. But if someone does that, it shows a lack of sportsmanship and I think they should be "outed."