Under monopolistic competition as the products are differentiated, the producer has to incur expenses to make his brand popular. The expenditure involved in selling the product is called “selling cost”.
According to Prof. Chamberlin, selling cost is the cost incurred in order to alter the position or shape of the demand curve for a product.
Under perfect competition and monopoly, there is soiling COM.
(Eg.) Advertisements, Free services, Home delivery, etc.