Any person, firm or corporation advertising for sale at retail an article or commodity not available during any day of the advertised period, shall, on demand of the customer, issue a "Rain Check" which will permit the customer to purchase the advertised article or commodity at the advertised price within thirty days of the last offering date.
Ga. Comp. R. & Regs. R. 40-15-3-.13
O.C.G.A. Sec. 10-2-5 (Ga. L. 1972, p. 654).