This is absolutely priceless. I'm kind of split too (a la Graeme) - on one hand I think it's way over the top and wrong, but on the other.... BALLER!!
Ok, putting aside my personal feelings, I think that any screwing with someone's account would constitute as a bannable offense, so on this site, not a smart (or cool) move. However, according to the spirit of the game, I think this behavior could even be ENCOURAGED!! The premise is to win, and one could say, to win at any cost. Spying and gaining bargaining chips over your opponents should be paramountly approved by the nature of the game.
So overall, I think it's a fantastic tactic and I would potentially use it, or try and prevent it in every game I play, but not on this site - on here we submit to a harsher set of rules to keep the community going.