Ambiguity can be fun about the magical elements of the world. On one hand, it can be useful to draw us in, to introduce us to the strangeness slowly so that it seems natural. Adds mystery and wonder.
(Though, of course, that doesn't work if the character is (consciously) go about the magic. Having your POV character's actions lead only to ambiguous results does bad things to the plot.)
And sometimes it can be really, really, really fun to leave the question open. Not when it's the focus of the plot. If Jane Doe arrives at her grandmother's house to find out if it's really haunted, the story resolves when she learns whether it is and not one second sooner. On the other hand, if she arrived because her boyfriend dumped her and she lost her job and she can live more cheaply here while licking her wounds, you can insinuate that the woman who gives such good advice (or encourages her to stay hidden) is really her Great-Great-Great-Aunt Matilda who holed herself up in her home after she was jilted -- or a slightly batty neighbor who is fond of dressing up in vintage clothing -- without ever resolving it.
It can be a nice effect. It makes your story-world seem larger than your story is, because all of its wonders do not fit in your story.
I've run across some nice uses of this effect -- even in fantasy or SF where wonders are an accepted part of the world, where they tend to be the hand of a superior being, or not. Characters interpret things as divine guidance or as coincidence. Or a Chosen One who is propelled by the possibility of having divine protection and the certain knowledge that someone has to do something..
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