Now, if a pawn shop buys it off the guy, and the pawn broker sells it to you, that seems legitimate; the pawn broker buying a TV isn't unusual, nor is you buying it from the broker. You'll still lose the item because it's stolen, but you won't be charged. In-game, this is basically represented by purchasing from the AH; this protects you, since you have no reason to think an AH sale is illegitimate.
I'd rather see them handle it the way the guys at Valve handled AFKing for free hats/items. They figured out how to identify who was doing it, tracked it for a few weeks or a month, and then gave everyone who DIDN'T abuse it a free hat. Yes, there was a lot of QQ, but those to blame had no real recourse. Nor did they announce it beforehand, it was just a "Surprise! If you haven't been cheating, you get a free hat! If you have been, no hat!"
In this case, maybe an updated Deathcharger that can fly, for legitimate earners/purchasers alone. Those complaining that their duped copy can't fly will fall on deaf ears, because they should've known better, but they don't lose their mount. Those who earned it through raiding or gold legitimately get an even better version. Win/win.