We find evidence that customers evaluate services according to different rules depending on whether the overall service experience impression is negative or positive. The functional form by which the underlying service attributes are mapped into an overall satisfaction evaluation is compensatory in the former (negative) case and has conjunctive properties in the latter (positive) case. These findings are based on an examination of a large data set of outpatient healthcare customer satisfaction surveys. We conjecture that different cognitive processes are at work for positive versus negative service encounters.