I have no qualms with such techniques in these kinds of situations, especially at high REL's, but there is one glaring concern that comes up.
When I was a little level-0 Judgeling, my mentor taught me that we do not want players to feel like we are the “Magic Police.” In context, he was teaching me not to interfere just because something illegal *might* occur in a match I was observing, but the effect on player's psyches is broader and worth remembering. As great as it is to set up a sting operation to nab a cheater like this, we need to make sure to reduce the impact on other, rules-abiding players – and our PR – as much as possible. After all, we're a resource to players, not an adversary.
A) The “undercover” judge probably shouldn't make his presence known, even after he witnesses shenanigans. This both allows him to perform the same role later if needed and doesn't tip off other players that any spectator could be a Magic Gestapo. Instead, the undercover judge makes a beeline for someone on floor staff (who should know about the sting operation) and lets official floor staff pull the trigger on the investigation.
B) The philosophy of “Watch MtG” should continue in order to make players more comfortable with judge presence; specifically, judges watching matches without trying to “get” someone makes them more relaxed when we're around, and that's better for everyone.
C) Undercover judges should be used sparingly and with precise targets. The vast majority of Magic players have enough on their minds without worries that “Big DCI Brother is Watching You.”
Of course, there's a significant chance I'm dead wrong on this, but I wanted to share my thoughts.
Edited Benjamin Topping (July 17, 2013 12:07:40 PM)