It's pretty late so I might be wrong here, but I think theres a bug if you sneak an item that was due to show up in the showroom that refresh anyway.
I !took a venom grip, bought it when it stocked, it was still there after I bought it. Logged to another account that also needed a venom grip, tried to buy it and I got told "Other account beat you to it". Refreshed the page, still there, tried to take again and got the same message