That's really annoying. Perhaps you could ask for a refund?

Something like that happened to me years ago (another store - not ZiNG but I won't mention the name) when I was looking for a sealed copy of a game. The one I had in-hand had been opened, without shrink wrap. The staff member I spoke to instantly claimed it was the 'last one'. I looked a bit more carefully and there was a stack of sealed copies still on the shelf, hidden away.