No, not if the customer did not receive anything of value. If you bought something online, they took your money and a week later told you it is out of stock do you expect to pay the company for using their website? Of course not, that is ridiculous.

Edit - I actually work for a ticketing company (Entertainment/Sports), we've had to refund people due to event cancellations. We are not keeping people's money when the event is cancelled, as I said not only is that illegal it is downright stupid.