I'm going to have to take this riddle bait. My solution:

Move 1: weigh 6 coins vs 6 coins. Isolate the heavier set for the next move. Move 2: weigh 3 coins vs 3 coins. Isolate the heavier set for the next move. Move 3: weigh any two of the 3 remaining coins. If one is heavier, that is the counterfeit. Otherwise (if coins are equal in weight) the remaining coin is counterfeit.