John buys an old violin at a yard sale for $$10.$ He discovers from an appraiser that is worth $$200,000.$ The former owners notify him that the violin was sold by mistake as to its value and would like to have it returned to them and they will pay him $$50$ to rescind the sale. Under the circumstances, must John return the violin?

a$.$

Yes, mistakes as to value are material and he must return it and allow rescission;

b$.$

No$,$ mistakes, as to value, are not grounds for a rescission of contract;

c$.$

Yes, because it's only fair to allow rescission;

d$.$

No$,$ unless it is a mutual mistake of value;