With all this swapping of orders now it will be like a motorway queue with people changing lanes to get a few car(d)s ahead
The only fair way to do this is to offer a choice of whatever cards are in stock as a customer reaches the head of the master queue.
There is a whole new sales method here & that its a "I don't care, (click your maximum price limit box) & just instruct the seller to send out the first thing that becomes available to ship!
It might revolutionize the whole selling market, I would use it for one!