The problem of establishing and evaluating the credibility of travel narratives remained endemic in the early modern period, both for authors of accounts and their readers. Writers of 'authentic' reports needed to secure and defend their reliability in the face of doubts that they enjoyed a license to 'lie by authority' as a familiar proverb held. This essay investigates the strategies they employed for doing so, and the position of readers relying on a form grounded in ostensible eyewitness that they could not verify for themselves. However tempting it might have been to respond with scepticism and to consign this source of testimony to the farther removes of respectability, it constituted vital source material for cosmographers, historians, and anyone concerned to know the world and its diversity. Natural historians formed part of this constituency, and in the Royal Society figures like Robert Boyle and Henry Oldenburg developed protocols and practices for improving the accuracy of observation. The risk of error did not disappear, but it could at least be managed.