Spending Habits

The Carbolic Smoke Ball Co. made a product called the "smoke ball". It claimed to be a cure for influenza and a number of other diseases, in the context of the 1889–1890 flu pandemic (estimated to have killed 1 million people).
The Company published advertisements in the Pall Mall Gazette and other newspapers on November 13, 1891, claiming that it would pay £100 to anyone who got sick with influenza after using its product according to the instructions provided with it.
Mrs Louisa Elizabeth Carlill saw the advertisement, bought one of the balls and used it three times daily for nearly two months until she contracted the flu on 17 January 1892. She claimed £100 from the Carbolic Smoke Ball Company. They ignored two letters from her husband, a solicitor. On a third request for her reward, they replied with an anonymous letter that if it is used properly the company had complete confidence in the smoke ball's efficacy, but "to protect themselves against all fraudulent claims" they would need her to come to their office to use the ball each day and be checked by the secretary. Mrs Carlill brought a claim to court. The barristers representing her argued that the advertisement and her reliance on it was a contract between her and the company, and so they ought to pay. The company argued it was not a serious contract.
JUDGMENT
The Court of Appeal unanimously rejected the company's arguments and held that there was a fully binding contract for £100 with Mrs Carlill. Among the reasons given by the three judges were (1) that the advertisement was not a unilateral offer to all the world but an offer restricted to those who acted upon the terms contained in the advertisement (2) that satisfying conditions for using the smoke ball constituted acceptance of the offer (3) that purchasing or merely using the smoke ball constituted good consideration, because it was a distinct detriment incurred at the behest of the company and, furthermore, more people buying smoke balls by...