What is credibility? In regard to eyewitness accounts of cryptids, this gets complicated, for eyewitness-credibility and description-of-cryptid credibility often become intertwined. Let’s get them separated.
Consider how a witness speaks and acts under questioning, if you’re serving on a court jury; the witness might seem believable. Now consider an eyewitness of a cryptid that you feel sure could not exist; do you look for anything that might indicate the person is telling a lie or misidentifying a non-cryptid? It is hard, sometimes, to be objective, when our feelings or basic beliefs appear to be threatened by the testimony of what has appeared to another person. We are all human, regardless of what the cryptid is.
How rare the evaluator who can separate the eyewitness-credibility from the description-of-cryptid credibility! If we feel that a large hairy ape should not be living in North America, we might notice little mannerisms or hesitancies in the testimony of a Big Foot eyewitness. If we feel that all species of pterosaurs should be extinct, we might question the religious motivations of the eyewitness of an apparent Rhamphorhynchoid pterosaur (most of those interviewers are creationists). We would do well to avoid rushing to a convenient conclusion, keeping an open mind to discovery, even when it means changing an old, deep-seated assumption.