When one listens to any anecdote from another, we listen in regard to what it means to us. So with a story like going to the shops and buying some items, it doesn’t mean anything to me unless I know you personally. This might be because some of the items I will eat or some other reason. Even my close friends don’t tell me things like that unless there is some relevance to something else they are telling me to me, even if it is to make me laugh because of some situation that happened, or unless I requested to know what they did during the day out of interest in them, on the grounds of friendship with would be a mutual interest in fact.
Some people lie and make things up for attention as with a tiger anecdote for example but if they are a friend of mine, I will probably know if that is the kind of person they are and not believe them particularly if there are no witnesses. But what if they are not and still tell me the tiger story in seriousness? Then I might believe them. So credibility of the person themselves plays a part also. This credibility is only established though a long a fruitful friendship and doesn’t apply to most people. Even if the story is from a stranger and mundane, about biscuit shopping I probably won’t believe them because I will be wondering what they are getting out of telling a complete stranger such a boring thing.
If a stranger or a trusted friend told me they saw a man change into werewolf, the issue with the stranger is obvious but the issue with the trusted friend is different. It’s not going to be me doubting their story but doubting their perception and interpretation of what they saw. Now multiple witnesses would help but not very much in this case because it isn’t to do with establishing credibility or honesty. An optical illusion can fool many people for example! The issue in this context is more about extraordinary claimed needing extraordinary evidence as you mentioned. The reason is because what is reported is not only unusual but contradictory to how the world works. The only way a man could be seen to change in such a way is if it was some kind of illusion. If an illusion then the integrity of how the physical world works is intact.
However this fails to take account of the form and nature of paranormal occurrences and the extent of human knowledge about how the world works. Some people think that all things that exist are physical and so science can in theory explain them, even if we don’t have all the answers right now. Others disagree with this view, and there is some evidence for both sides of this debate. The issue is the interpretation of the evidence, which is a familiar theme of course in this context. It is quite possible however that the world works in more than one way or to put it another way the world is both physical and something nonphysical in nature. When specific information from some forms of paranormal phenomena is gained by two or more witnesses and independently of each other, and this gets confirmed by whoever it is in a position to confirm it, then it provides evidence not only of the phenomena but that the universe has more than one level of operation only one being physical in nature and amenable to scientific analysis.
There are cases where verifiable information can be corroborated by more than one independent witness but as with all things, it’s the quality and credibility of the witnesses that counts more than evidence itself. This is even more the case with things that cannot be demonstrated in a lab in front of witnesses because what is seen or experienced is not operating according to physical laws. The laws are unknown. However they often have a theme which normally doesn’t include actual physical human beings turning into werewolves, because it isn’t about physics. Often it is to do with information perceived within a person than can sometimes be correlated to reality and witnesses.
