It's a cool concept. Basic, but it has a lot of potentials. If u increase the speed in which one has to sell their ticket, it gets an even better flow and difficulty.
Love the artworks! But it is a bit easy to recognize which customer is a ghost. It would be better if the hints get subtler over time. Or maybe u could include dialogs where u have to find out who is a ghost by asking clever questions.
Good work!