No additions whatsoever shall be made to the stock of goods, wares or merchandise set forth in the inventory attached to the application for the permit required hereunder, and nothing shall be offered for sale or sold at any such sale which is in addition to the stock of goods, wares or merchandise described in such inventory. Under no circumstances shall the inventory offered for sale exceed by fifty percent the average inventory carried by the applicant over the preceding five years, or, if such applicant has been in business for a lesser period of time, then such inventory offered for sale shall not exceed by fifty percent the average inventory carried for the period of time the applicant has been in business. Any abnormal purchases during the year prior to the application for a permit shall be cause for refusal to issue the permit.