In the scenario we need to find evidence of the formation of a contract between Mary and Harry, to establish if Mary has a case against Harry. Contracts are generally formed when two parties exchange promises and have reached an agreement.

However in the contrasting case of Carlill v Carbolic Smoke Ball Co, where the defendant placed and advertisement offering for sale smoke balls, they also promised that anyone who used the smoke ball and caught flu would receive £100, a £1000 had been placed in a bank to show to their sincerity in the matter. The claimant, Mrs Carlill, bought the smoke ball and caught flu. She sued for her £100. It was held that the offer was made to the whole world and was not an invitation to treat. Lindley LJ, stated in his judgement advertisements offering rewards are ‘offers to anybody who performs the conditions named in the advertisement and anybody who perform the condition accepts the offer’ . It was also recognised by Lindley LJ that the wording of the advertisement expressly showed a offer by the offeror. In Harry’s advert ‘…will be sold to the first 12 replies received enclosing a cheque for £75…’ it suggests that a performance or completion of a task is required, sending the cheque. Mary has fulfilled the criteria asked for in the advertisement and has therefore entered into a contract with Harry. As it is a unilateral contract notice of the acceptance to Harry is not required Lindley LJ stated ‘the person who makes the offer shows by his language and from the nature of the transaction the he does not expect and does not require notice of acceptance…’ therefore Mary has entered into the contract and completed her performance.

Harry could argue that he had withdrawn the offer; by placing another advert in the same newspaper on the 6th January. The general rule regarding revocation is that it must reach before acceptance and be effectively communicated to the offeree. In Byrne v Van Tierhoven on 1st October the defendant posted an offer in Cardiff to the claimants in New York. On 8th October the defendant posted revocation of the offer.then on the 11th October the claimants sent a telegram accepting the offer then later on the 15th sent confirmation in a letter. On 20th October the claimants received the letter dated the 8th. It was held that the defendants revocation was inoperative because it did not reach the claimants before they had accepted the offer. In unilateral contracts it is more difficult to revoke  an offer because it has to be revoked from the ‘whole world’. In the American case Shuey v US 92 U.S. 73 (1873), which can be used as persuasive authority in the English courts. Mr Justice Strong said in his opinion ‘it was withdrawn through the same channel in which it was made. The same notoriety was given to the revocation that was given to the offer’ . He is saying revocation should be made in the same way the offer is made. Harry revoked the offer in the same way as he published it by placing an advert for both in the Bruddersfield Gazette. Therefore he generated the same notoriety or publicity to both offer and the revocation of the offer.

Harry could argue successfully that he revoked the offer effectively.

Mary needs to be prove the ‘Postal Rule’. It is said to be a rule of convenience. ‘Acceptance is valid when posted even if the letter is incorrectly addressed or lost and never arrives’ this rule is well illustrated in Adams v Linsell where the defendant wrote to the claimants offering to sell wood and wanted a reply ‘in course of post’. On 5th September the offer reaches the claimants and then on the 8th the defendants sell the wood to a third party. On the 9th September acceptance letter from the claimants arrive. It was held that there was a valid contract because acceptance was made on the 5th September when the letter was posted not when it arrived on the 9th. However there are exceptions to the postal rule. The first exception is; if a letter is handed to a postman it is not posted as he is only authorised to deliver post. The next exception is; if a letter is not properly addressed it is not valid. The next exception which is relevant to this situation is in the case of Holwell Securities v Hughes where the legal principal was established that if an offeror requests to see the acceptance then it is not valid until it is received by the offeror. Following the decision in Adams v Linsell Mary would have a valid contract under the postal rule as she sent her acceptance on the 6th and acceptance is valid when sent not received. However relating the exception established in Holwell Securities v Hughes  the exception does apply and the postal rule cannot be used. Harry has excluded from the unilateral contract the postal rule with the wording ‘first 12 replies received’. He has stipulated that he wants to receive the acceptance so it is not valid when it is posted it is valid when it is received. Harry did not receive Mary’s acceptance until 7th January which is too late as the offer had been revoked on the 6th January.

It is up the courts as to whether Harry can rely on the postal rule or not.

Mary’s offer did not correspond exactly with the offer that was made. Harry’s advert asked for a £75 cheque, whereas Mary sent £75 cash. This could be a counter offer as acceptance should be an unqualified acceptance of all the terms of the offer. The leading case is Hyde v Wrench, where on the 6th June the defendants offered the claimants a farm for sale fro £1000 and the claimants made a offer of £950. On the 27th June the defendants rejected the counter offer, then on the 29th the claimants made a purported acceptance of the 6th June offer of £1000. it was held that there was no contract because the original offer to sell had been ended by a counter offer of £950. As in this case and other counter offer cases the actual counter offer is normally when a lesser sum of money is offered instead. That isn’t quite the same issue here. The difficulty is not that a lesser amount was offered but that the exact method of payment was not met. There are no leading cases currently where this kind of situation has occurred. It would be at the courts discretion whether Mary’s acceptance was valid or void, due to the fact that it did not correspond exactly with the offer.