Section 13. (a) The term ''cost to the retailer'' shall mean the invoice cost of the cigarettes to the retailer, or the replacement cost of the cigarettes to the retailer within thirty days prior to the date of sale, in the quantity last purchased, whichever is lower, less all trade discounts except customary discounts for cash; to which shall be added the cost of doing business by said retailer as evidenced by the standards and the methods of accounting regularly employed by him in his allocation of overhead costs and expenses, paid or incurred, and must include, without limitation, labor (including salaries of executives and officers), rent, depreciation, selling costs, maintenance of equipment, delivery costs, all types of licenses, taxes, insurance and advertising.

(b) In the absence of proof of a lessor or higher cost of doing business by the retailer making the sale, the cost of doing business by the retailer shall be presumed to be twenty-five per centum of the invoice cost of the cigarettes to the retailer, or of the replacement cost of the cigarettes to the retailer within thirty days prior to the date of sale, in the quantity last purchased, whichever is lower, less all trade discounts except customary discounts for cash.

(c) The term ''cost to the wholesaler'' shall mean the basic cost, which is defined as the invoice cost to the wholesaler, plus the face amount of the state cigarette excise or the replacement cost of the cigarettes to the wholesaler, plus the face amount of the cigarette excise within thirty days prior to the date of sale, in the quantity last purchased, whichever is lower, less all trade discounts except customary discounts for cash; to which shall be added a wholesaler's mark-up to cover in part the cost of doing business, which wholesaler's mark-up, in the absence of proof of a lesser or higher cost of doing business by the said wholesaler shall include all direct costs attributable to the receiving, bonding, stamping, handling, storing, sales and delivery of cigarettes, and, shall additionally include as evidenced by the standards and methods of accounting regularly employed by him in his allocation of overhead cost and expenses, paid or incurred, including without limitation, labor, salaries of executives and officers, rent, depreciation, selling costs, maintenance of equipment, delivery, delivery costs, all types of licenses, taxes, insurance and advertising, shall be two per centum of said basic cost of the cigarettes to the wholesaler, except for sales to chain stores which shall be one-half per centum, plus cartage to the retail outlet if performed or paid for by the wholesaler, which cartage cost shall be deemed to be three-fourths of one percent of the basic cost of the cigarettes to the wholesaler, unless said wholesaler claims and proves a lower cartage cost, or of the replacement cost of the cigarettes to the wholesaler within thirty days prior to the date of sale, in the quantity last purchased, whichever is lower, less all trade discounts except customary discounts for cash.

For the purpose of this subdivision, the term ''chain store'' shall mean any person or persons who own or maintain ten or more retail outlets in the commonwealth, having one hundred percent common ownership or any vending machine operator who operates vending machines in twenty-five or more locations.

(d) In the absence of proof of a lesser or higher cost of doing business, the cost of doing business to the retailer, who received in connection with the retailer's purchase not only the discounts ordinarily allowed upon purchases by a retailer but also in whole or in part the discounts ordinarily allowed upon purchases by a wholesaler, shall be presumed to be twenty-five per centum of both the invoice cost of the cigarettes to such retailer or the replacement cost of the cigarettes to such retailer within thirty days prior to the date of sale, in the quantity last purchased, whichever is lower, less all trade discounts except customary discounts for cash and ''wholesaler mark-up.''

(e) In all advertisements, offers for sale or sales involving two or more items at a combined price, and in all advertisements, offers for sale or sales involving the giving of any concession of any kind whatsoever (whether it be coupons or otherwise), the retailer's or wholesaler's selling price shall not be below the ''cost to the retailer'' or the ''cost to the wholesaler'', respectively, of all articles, products, commodities and concessions included in such transactions.

(f) The terms ''sell at retail'', ''sales at retail'' and ''retail sales'' shall mean and include any transfer of title to tangible personal property for a valuable consideration made, in the ordinary course of trade or usual prosecution of the seller's business, to the purchaser for consumption or use. The terms ''sell at wholesale'', ''sales at wholesale'' and ''wholesale sales'' shall mean and include any such transfer of title to tangible personal property for the purpose of resale.

(g) The wholesaler, vending machine operator, transportation company or unclassified acquirer who purchases cigarettes directly from a manufacturer or from a wholesaler or unlicensed person, for sale at retail in determining ''cost to the retailer'' pursuant to subdivision (a) of this section shall add the ''wholesaler's mark-up'' to the invoice cost of the cigarettes to said retailer, or the replacement cost of the cigarettes to said retailer within thirty days prior to the date of sale, in the quantity last purchased, whichever is lower, less all trade discounts except customary discounts for cash, before adding the ''retailer's cost of doing business''.