Final answer:
The sales associate should assist the customer by engaging in conversation to understand their preferences and providing information about the unique features of the sweaters, helping the customer make an informed decision.
Step-by-step explanation:
The best way for the sales associate to respond to a customer comparing two similar sweaters is to engage in a collaborative exercise by asking open-ended questions to determine the customer's needs and preferences. The associate could highlight the unique features of each sweater, such as the material, fit, or style, and compare this to the customer's expressed preferences to guide their decision-making process. By providing personalized attention and professional advice, the sales associate can enhance the customer's shopping experience and help them decide which sweater would be the best choice for them, applying the concept of comparing marginal utility in a real retail scenario without the explicit use of utils.