What is the fiduciary duty of an individual in a relationship where there is no written agreement or binding agreement?

Any intelligent discussion of fiduciary duty starts with what is required in fact for there to be such a duty. The starting point is the judgment of Wilson J. (dissenting only in the result) in Frame v. Smith, 1987 CanLII 74 (SCC), [1987] 2 S.C.R. 99, p. 136: Relationships in which a fiduciary obligation have been imposed seem to possess three general characteristics: (1) The fiduciary has scope for the exercise of some discretion or power. (2) The fiduciary can unilaterally exercise that power or discretion so as to affect the beneficiary’s legal or practical interests. (3) The beneficiary is peculiarly vulnerable to or at the mercy of the fiduciary holding the discretion or power.