I got the following from an eBay seller:


I am writing as unfortunately we are out of stock of all of the items that you have ordered. Due to large amount of orders we receive and eBay allowing customers to buy items without paying immediately. It is very difficult to have correct stock levels at the time of customers placing orders. Unfortunately we do not currently have a system for holding orders so we will refund you for your order. We are very sorry for any inconvenience this may cause you.


I haven't yet worked out how anyone can buy stuff without paying immediately..