The development of new approaches for assessing service quality is a priority for both managers and scholars. Until now, the most widely used tool for evaluating service quality is the SERVQUAL. It is based on a disconfirmation pattern, according to which service quality depends on measures of gaps between customer expected and perceived quality; the gaps come from the answers provided to a questionnaire representing fixed quality dimensions (tangibles, reliability, responsiveness, assurance and empathy). Notwithstanding its widespread application, the SERVQUAL has been theoretically and operationally criticised for the invariance of its dimensions across contexts. In contrast to the SERVQUAL and to other unchangeable techniques proposed in previous quality management researches, in this article, we propose a methodology able to assess service quality by means of firm-specific quality dimensions. Particularly, employees’ knowledge is exploited to collect the critical success factors (CSFs) of a company; subsequently, the measurement and management of a company service quality is performed by gathering customer expectations and perceptions, according to the collected CSFs. Total quality management (TQM) has, from long ago, established procedures for managing customer perceived quality but, in this study, an application for overcoming the lack of a systematical implementation of employee knowledge in TQM practices is proposed. This research is explorative in nature and a statistical support for our methodology is provided by an exploratory factor analysis. The results confirm that employees are able to gather quality dimensions customers value and that these dimensions can be successfully employed into a flexible tool for assessing and managing service quality. Moreover, according to the proposed methodology, the evaluation of service quality may change as well as CSFs of a company change; finally, managers may support TQM of a company by monitoring its provided quality on the basis of CSFs.