How does one deal with the possibility of deception? Extant literature has mostly focused on identifying deception via cue detection. However, how we reason about the possibility of deception remains under-explored. We use a novel formalism to expose the complexity of this reasoning problem (e.g. separating the uncertainty of an honest mistake, from willful deception), in the process highlighting several reasoning errors regarding deception. Notably, we show reasoners to make substantial errors when reasoning about a (possibly) deceptive source in isolation (including base rate neglect errors), but find that reasoning improves when further (independently sourced) corroborative or contradicting reports are introduced.