The chapter investigates the interaction effects between the search strategy of software agents and the consumer’s product class knowledge in the context of consumers seeking to purchase cars on the Internet. The research design used was a 2 x 4, between groups, completely randomized, two-factor, factorial design. The independent variables which were manipulated were product class knowledge (HIGH KNOWLEDGE, LOW KNOWLEDGE) and agent search strategy (elimination by aspects (EBA STRATEGY), weighted average method (WAD STRATEGY), profile building (PROFILE STRATEGY), simple hypertext (HYPERTEXT STRATEGY)). The dependent variables which were measured were satisfaction with the decision process (SATISFACTION), confidence in the decision (CONFIDENCE), trust in the agent’s recommendations (TRUST), propensity to purchase (PURCHASE), perceived cost savings (SAVINGS), and cognitive decision effort (EFFORT). Significant differences were found in the affective reactions of the subjects toward the agent/application depending on the level of product class knowledge possessed by the subjects. Subjects with high product class knowledge had more positive affective reactions towards agents/applications which used the WAD and EBA strategies as compared to the PROFILE strategy. Subjects with low product class knowledge had more positive affective reactions to agents/applications which used the PROFILE strategy as compared to the EBA and WAD strategies. When the systems were modified to increase the amount of information provided and to increase the degree of control provided to the subjects, their affective reactions to the agents/applications were found to be different from the original study. Subjects responded more positively to the previously “less preferred” strategy, thus weakening the interaction effect.