In Morr v. Crouch (1969), 19 Ohio St.2d 24, the Ohio Supreme Court held:

An attorney who is without special authorization has no implied or apparent authority, solely by virtue of his general retainer, to compromise and settle his client’s claim or cause of action.

This means that an attorney must get his/her client’s authority (permission) to settle the client’s case.  Therefore, the client has the ultimate say in whether his/her case is settled, and for how much.