While this is hardly a matter of life and death, I largely agree with Gooner. Retailers taking payment before confirming stock is available is easy to avoid and just wrong. Mr Retailer, by all means take my order before you are 100% sure you have stock, but do not take payment. It isn’t hard to verify payment before picking an order, and then taking payment once with order has been picked and is ready to ship. It SHOULD be standard practice for all retailers.
All of that said, On-One’s informal approach to customer service is pretty well known. In fact, they advertise it themselves, so this sort of minor customer service issue shouldn’t cause too much anger.