With regards to the case of Susan, whether she may successfully sue Elizabeth or not, there is no precise answer. It depends if the contract is effective or not. For a contract to be valid, there are four key elements, which are "offer", "acceptance", "consideration" and "legal intention". Without any one of them, there is no contract at all and the agreement cannot be legally enforceable --- and this is the main area where this case concentrates on.
In this case, Elizabeth placed an advert to sell her bike, which was an invitation to treat. When Susan asked her about the price, Elizabeth invited Susan to make an offer of no less than Ã¢ÂÂ¤50. Before long, Susan replied by making an offer of Ã¢ÂÂ¤50 to buy Elizabeth's bike. Up to this point, it is crystal clear that there is no contract between them, since there is an offer but no acceptance of the offer.
After knowing the offer, Elizabeth spoke to John that she would like to sell the bike to Susan at Ã¢ÂÂ¤50, yet she had never told Susan about this. John then notified Susan about it. Under this circumstance, this raised a question, "Does acceptance exist?" Shortly, Elizabeth changed her mind and decided to raise the price to Ã¢ÂÂ¤150 under the influence of her mother. She then left this message on Susan's answering machine. At this moment, another question arose, "Does counter offer exist?" Susan read the message; still, she brought Ã¢ÂÂ¤50 for the bike. A new question appeared, "Does consideration change?" Susan's reason for doing so was that she believed they had an agreement of Ã¢ÂÂ¤50. Finally, there is one last question, "Does legal intention exist?"
As a matter of fact, only if the four key elements really there, the contract is valid and hence Susan can...