On the tech side there's definite things that you could do to get around that and I'd expect some sort of real-time communication would be necessary to track al

On the tech side there's definite things that you could do to get around that and I'd expect some sort of real-time communication would be necessary to track all that stuff, but there are companies that handle that sort of thing pretty cheaply like pusher/pubnub/bashoto. I'd be surprised if they get more sales without it, if they are only showing available stock values when they are below a certain threshold, say ten items.