There are a number of models which try to capture and define "Service Quality". They each have their strengths, and weaknesses. In the end though the core definition is simple and consistent:

Service quality is:
Customers thinking they're getting better service than expected.

This is often referred to as the perception gap. i.e the gap between what the customer expects and what they think they got. It's worth noting that both sides of the gap are in the customers mind. You may actually deliver better service then your competitors, but if the customer thinks that your service is worse then that's all that matters.

Because the perception gap is based on the difference between what a customer expects to receive from a service and what they think they received both sides of the gap are "soft" – they are based on customer impressions rather than a "hard" definable quality. This means the perception gap is difficult to measure, difficult to manage and is likely to change with time and experience. nevertheless it's vital to business success.

Before considering quick wins and strategic improvements there are a number of key questions which contribute to our understanding of the perception gap. These models are the result of significant research:

RATER: What are the key criteria that customers use to measure service quality

The GAP model: What are the corporte processes involved in managing and changing the perception gap and what strategic changes must an organisatiopn make to improve service quality

The Kano model: What do customers expect as a minimum standard,
what actually makes a difference if you do it better?

Grönroos' Perceived Service Quality model: What actually creates expectations and perceptions
Mäkelin and Vepsäläinen and Gale: How do perceptions change with time


Servqual: How can an organisation measure service quality