It is hereby declared that advertisement, offer to sell or sale of any merchandise, either by retailers or wholesalers, at less than cost as defined in this act with the intent of unfairly diverting trade from or otherwise injuring a competitor or with the result of deceiving any purchaser or prospective purchaser, substantially lessening competition, unreasonably restraining trade or tending to create a monopoly in any line of commerce is an unfair method of competition contrary to public policy and in contravention of the policy of this act.