I won't even bring a game to a show with a penalty. If I buy a game and want to take it right away I won't pay a penalty even if there is one. As the buyer I never agreede to bring my game and leave it. The seller made that commitment, its not incumbant on the buyer to pay anything more than the selling price. If I was stopped I would get the police involved if need be. MGC does it well, you get an incentive to leave it, rather than a penalty for removal.
Once a game is sold though the free admission for the original owner should be revoked and transferred to the buyer if they leave the game.