The holes don't have to be the physical location where the goods were sold. It's just where they're stored. Think of the lots at a big auction, arranged in rows behind the bidding house/tent. You bid on a standardized lot and when you win it you go collect your goods from stall X, which you might have inspected before the sale. That's similar to what the authors are proposing here for markets, which is only one of a number of possibilities they offer.