The buyer–seller relation has become an integral part of business strategy in the service sector. This study begins from the importance of quality of service in the buyer-seller relation and adds evidence concerning an issue missing in other studies performed: the importance that clients attribute to dimensions of perceived quality varies as a function of the length of their relation to the firm. We identify which dimensions of quality of service should at any given moment be the primary concern of management and which should have secondary significance. To do this, we contacted an experienced national consultancy in order to learn, by means of a multiple linear regression model, the value attributed on the part of its clients to the quality of service and its dimensions. The study shows how buyers value some dimensions of perceived quality as a function of the length of their relation to the organisation.