Customer Satisfaction research which involves questioning actual customers to gather their opinions of the service they have received has an important place in the overall understanding of the service offered. However it is subjective and will not provide a positive discriminator of services.
Customers find it difficult to divorce the history of service experience from the actual most recent store visit. That is to say, "if they expect poor service they are likely to complain that they receive poor service" no matter how high the standards actually are.