While George was visiting his Doctor, he mentioned that he wished to sell his expensive sailboat. The Doctor expressed an interest in buying the boat, and offered to pay George $10,000 for it. George had intended to advertise the boat for $12,000 in the local newspaper, but agreed to sell it to the Doctor for $10.000. Some weeks after the boat had been sold; George wished to avoid the contract. What could George argue to avoid the contract? What would the Doctor need to prove