24. Fees are fair and reasonable if they are warranted in the circumstances and are proportionate to the services rendered. In particular, a member shall take the following factors into account when determining his fees:
(a) his experience;
(b) the time required to execute the mandate;
(c) the difficulty of the mandate;
(d) the importance of the mandate;
(e) the liability assumed;
(f) the need to perform unusual services or services requiring exceptional competence or speed.