Bo Bennett describes an "anecdotal fallacy" as an "argument from hearsay":
Presenting the testimony of a source that is not an eyewitness to the event in question. It has been conclusively demonstrated that with each passing of information, via analog transmission, the message content changes. Each small change can and often does lead to many more significant changes, as in the butterfly effect in chaos theory.
For an argument to be logically fallacious for Bennett it must be a commonly applied, deceptive error in reasoning. Not all anecdotal evidence would lead to a fallacious argument.
Wikipedia shows that anecdotal evidence can be important such as in case studies:
Anecdotal evidence is evidence from anecdotes, i.e., evidence collected in a casual or informal manner and relying heavily or entirely on personal testimony. When compared to other types of evidence, anecdotal evidence is generally regarded as limited in value due to a number of potential weaknesses, but may be considered within the scope of scientific method as some anecdotal evidence can be both empirical and verifiable, e.g. in the use of case studies in medicine. Other anecdotal evidence, however, does not qualify as scientific evidence, because its nature prevents it from being investigated by the scientific method.
Someone who is an eyewitness of either a spirit or a murder does not fall under the argument from hearsay definition. They are not a third party reporting the evidence in a casual or informal manner. They are the eyewitnesses.
Here is the final question:
And why is the claim of seeing a spirit met with far more skepticism than the claim of seeing a murder?
C. S. Lewis claims regarding miracles: (page 2)
What we learn from experience depends on the kind of philosophy we bring to experience.
Those who have more skepticism regarding seeing a spirit than witnessing a murder are expressing their philosophic view that seeing a spirit is more unlikely than witnessing a murder.
Bennett, B. "Argument from Hearsay". Retrieved from Logically Fallacious on April 16, 2019 at https://www.logicallyfallacious.com/tools/lp/Bo/LogicalFallacies/52/Argument-from-Hearsay
Lewis, C. S. (1947). Miracles; a preliminary study.