(a) A promotional practice must be in the public interest. In determining whether a practice is in the public interest, the Commission shall consider the following:

(b) No public utility shall, directly or indirectly, in any manner or by any device whatsoever, offer to any person any form of promotional practice except such as is uniformly and contemporaneously extended to all persons in a reasonably defined class. No public utility shall, in the offering of a promotional practice, give any undue preference or advantage to any person or subject any person to any undue prejudice or disadvantage. No public utility shall establish or maintain any unreasonable difference in the offering of promotional practices either as between localities or as between classes to whom promotional practices are offered. No public utility shall classify the persons to whom its promotional practices are offered except to the extent permitted by the laws of this State.

(c) All advertising associated with a promotional practice shall be truthful and not misleading or deceptive.