Sylvia, an elderly widow who is almost deaf, owns her own home. Her closest confidant for business transactions is her son-in-law, Ron. Ron offered to purchase her home for $500,000. The home had recently been appraised at $600,000, but Sylvia agreed, in writing, to sell when Ron persisted in making the offer. She never asked and he never volunteered information about the appraised value of the house. If Sylvia later desires to set aside that sale, what is her best argument against the validity of the contract?