Final answer:
Retailers should specify a specific category or business line to focus their core competencies and create product differentiation, which can lead to a stronger brand and competitive advantage.
Step-by-step explanation:
When choosing a line of business, retailers should specify a specific category in which to operate. This decision often aligns with the concept that businesses which focus on a core competency or a narrow range of products tend to be more successful.
The degree of product differentiation and the ability to offer a unique variety in the market can contribute to building a well-respected brand name and compete in a realm closer to monopolistic competition rather than perfect competition.