In the context of evaluating service quality, assurance refers to the knowledge and courtesy of employees and their ability to convey trust. Assurance is defined as having confidence in one's abilities and a promise, guarantee from others. In the context of evaluating service quality, having assurance means you can trust that the quality of the service being provided will be to the best of the organizations abilities. You never want to feel like you aren't sure if the quality of service you're going to be paying for may or may not be great.