Cheating with ghosts - thoughts??

Just played a game where I was the last imp and there were two crew left. The crew weren't 100% sure I was imp and asked the ghosts to leave if I was imp. A ghost left and they voted me out. This is cheating, right?? Like WTF. Then the crew gloats as if they just figured it out on their own. So, question is - is it fair to use ghosts in this sense??