When making personally relevant decisions (e.g. on health-related issues), laypersons have to deal increasingly with science-based knowledge claims that are frequently not only inconsistent if not contradictory but also beyond their own everyday understanding. Nevertheless, they need to reason about these issues. The present interview study investigates the concrete reasoning about and resolution of a scientific conflict between knowledge claims put forward by medical experts in 21 laypersons and 20 intermediately knowledgeable persons. Results showed that explanation patterns were influenced by assumptions about not only the tentative nature of knowledge but also about the person of the expert and the institutional practice of science. When trying to resolve the conflict, both groups reported significantly more strategies of evaluating and validating the source rather than assessing the claim's veracity based on their own understanding. Hence, when facing scientific conflicts, source validation and deference to another's expertise is rather the rule than the exception. Modern societies are based on an elaborate division of cognitive labor, underlining the need to evaluate the social context in which knowledge claims are derived. The discussion derives implications for learning and instruction.