If that was the intention, then there could just be a counter indicating how many had been purchased by others, but it only needs to appear if that is non-zero.

If that was the intention, then there could just be a counter indicating how many had been purchased by others, but it only needs to appear if that is non-zero. That seems like the far more obvious way to do it. I don't know how you get to the "0 of 1" strategy without trying to trick people. The 1 is completely made up.