The real question though, is thus:
Let's say for argument's sake that you have a £500 credit card limit. You then order an iPhone 5 online along with the customary 4 week wait. Apple pre-authorises your card and it's maxed out.
Then, you manage to get hold of an iPhone 5 in-store. You go to use your credit card.
Question: does it get declined or do you walk out with an iPhone?