If you are applying for a job in a Costco store, then your answer should be very receptive to this type of task! The interviewer wants to hear that you are comfortable conversing with other people. As a customer service person, you are definitely a sociable person. Explain to the interviewer that you enjoy getting to know your co-workers, work hard to build relationships with your regular customers through simple interactions, and look forward coming to work each day in customer service. You might work best in a large group setting, or one-on-one interactions might be your thing. Either way, you are a sociable person, and you are okay promoting products to members.
"I think it would be great fun to converse with Costco members, encouraging them to try new products. I also think it would be enjoyable to gather feedback and thoughts on the customers' reactions to new products."