Philomena owns a bookshop which specialises in acquiring and selling rare books. She recently saw an advertisement in a specialist book magazine for a first edition of a book written by Niccolò Machiavelli. The advertisement, which had been placed by Mark Harrington of Harrington’s Rare Books, stated that it was ‘on offer for £1000’. Philomena telephoned Mark on Monday morning. She informed Mark that she would buy the book for £750. Mark replied that he would sell it for £900. Philomena responded by saying she would need some time to think about buying the book for £900. Mark informed Philomena that he would not sell the book to anyone else until Philomena phoned him back in three days’ time with her final decision.