Successful marketing efforts and professional sales encounters often depend on consumer involvement in the purchase decision process itself, which in turn may impact firm performance. Despite the importance of consumer involvement, research has yet to fully explain the relationship between consumer personality characteristics and the nature of consumer purchase involvement. This study explores the degree to which consumer perception of salesperson ethical treatment helps explain the relationship between consumer personality characteristics and nature of involvement. Data were collected from a large sample of working adults placed in two scenario-based positive professional sales encounters featuring an important purchase decision. The results indicated that adult consumers’ personality characteristics functioned through judgment of salesperson ethical treatment to affect the nature of purchase involvement. Specifically, consumer judgment of salesperson ethical treatment fully mediated a positive relationship between internal locus of control and cognitive involvement. By comparison, consumer judgment of a salesperson ethical treatment partially mediated the positive relationship between emotional awareness and cognitive involvement. The above findings were similar for informational and relational salesperson customer-orientated scenarios. Key implications for selling professionals and sales organizations are discussed, such as augmenting consumers’ self-assessments to increase their perceptions of salesperson ethics and purchase involvement. The limitations and recommendations for future research are also presented.