First time I have ever seen one of these. A "car boot sale" in a shop, minus the car of course. It's on Abergele Road in Colwyn Bay. If anyone has any bits and bobs to sell you wander it, pay a fee, presumably daily, and spread your stuff out. Considering its early November there were a reasonable number of customers wandering around.
I don't imagine this ever spreading to Mostyn Street but I suppose it's preferable to an empty shop in a less desirable retail area