Quotes from the email I have just received from Amazon.co.uk:
… We are, therefore, delighted to confirm that we have reduced the price of Harry Potter 6 to just £8.99 (47% off) and that all our customers, muggles and wizards alike, will benefit from this reduction.
… and the new price will be magically changed in Your Account.
… Please note that the book will not fit through a standard letter box, so keep an eye out for our delivery owls.
… Thank you for shopping at Amazon.co.uk, and stay alert for You-Know-Who.
The mail looks just like usual Amazon notification simply informing me that the price reduction will affect the previously placed order. This kind of humour must be of British culture indeed.