The uneven distribution of knowledge within modern societies requires a reliance on sources (e.g., reference books, teachers, the Internet) in addition to own experience. Most scientific issues are far too complex to be understood in any depth by laypersons. Successful knowledge acquisition comprises the ability to vary the amount of sources used and to appreciate different sources in different contexts. Epistemological beliefs (i.e., learners' beliefs on the nature of knowledge and knowing) might affect this task. We report research on secondary school students' decisions about the amount of sources they would use and their source appreciation (the perceived usefulness of several sources), the impact of epistemological beliefs on such decisions, and their adaptivity to the contextual circumstances of the information search. After exposure to an experimentally induced epistemological sensitization, the students provided information on how they would proceed to confirm given knowledge. Study 1 explored the amount of sources (source quantity and access approaches). Study 2 investigated the perceived usefulness of several sources (source appreciation). Results showed an increase in the amount and appreciation of sources in a high-involving context and after sophisticated sensitization. More sophisticated beliefs led to a larger increase in the amount of sources in a high-involving context. Furthermore, epistemological beliefs predicted the difference in source appreciation between contexts. Conclusions are drawn for the use of sensitization and the teaching of digital literacy in schools.