Tell the interviewer that excellent member service is having a positive attitude and doing what it takes to ensure the customer comes back to your store. You might share that you think excellent customer service means having a smile on your face, saying please & thank you, and providing a great experience for the member.
"To me, great member service means that my customers are happier when they leave than when they initially arrived. I want every Costco member to feel like they received their money's worth from their membership commitment. This contentment should come from excellent service and variety in new products."