22. Unilateral mistake as to quality.

A fundamental mistake by one party1, not as to the terms, but as to the quality of the subject matter of the agreement does not invalidate the agreement2, or otherwise give ground for relief in equity3, even where the other party knows of the mistake4, unless in the circumstances he5 or his agent6 has misled the mistaken party, or his knowledge and failure to disabuse him amounts to equitable fraud7, or there is a duty to speak breach of which may found an estoppel8.

There are old cases of unilateral mistake where equity intervened because one party perceived the mistake