(a) In determining the cost of the stamper, cost of the retailer and cost of the wholesaler, the fact-finder shall receive and consider, as bearing on the good faith of such cost, evidence tending to show that any person complained against under any provision of this article purchased cigarettes with respect to the sale of which complaint is made at a fictitious price or upon terms or in such a manner or under such invoices as to conceal the true cost, discounts or terms of purchase. The fact-finder shall also receive and consider, as bearing on the good faith of such cost, evidence of the normal, customary and prevailing terms and discounts in connection with other sales of a similar nature in the trade area or state.

(b) Merchandise given gratis or payment made to a stamping agent, retailer or wholesaler by a cigarette manufacturer for display or advertising or promotion purposes, or otherwise, shall not be considered in determining the cost of cigarettes to the cigarette dealer if such practice is customary in the trade and offered to all dealers on an equal or proportional basis.