From looking at that picture, it looks like the oven is used. Seems like you might consider two options. The oven hasn't been out very long, so it is possible that the warranty is still in effect. Tell the owner you will buy it, but he/she needs to get replacement stone(s) (especially if the stones arrived broken and/or if the oven is still under warranty).
Alternatively, just find out the stone price from BS. I bought a replacement cooking stone for $20 shipped from BS - not a bad price, IMO.