How can I tell if a W.O.W. activation key has been used?

We had a tenant skip out quickly and left behind some items. One of these is a world of warcraft burning crusade collector's edition set. I am not familiar with these products, but from what I have found, there is a huge difference in new and used ( on resale value). It seems to be brand new, like they only opened the box, looked at it and then skipped town. Some of the Items are still shrink wrapped. How can I tell if the code is ociated with an account - without installing it on my pc?