The first red flag shows up in the very first sentence of the description, “Please read carefully before scheduling showings.” And you’ll want to read carefully, or you may almost miss the buried tidbit about the mystery tenant who has never paid:
"Upstairs apartment cannot be shown under any circumstances. Buyer assumes responsibility for the month-to-month tenancy in the upstairs apartment. Occupant has never paid, and no security deposit is being held, but there is a lease in place. (Yes, it does not make sense, please don’t bother asking.)"
Can you ever meet this person? How on earth does this no-pay lease work? Did said upstairs tenant have anything to do with this?
Various theories about this situation have been floated, including speculation that the "upstairs tenant" is actually a ghost and the sellers are trying to cover up evidence of a haunting. Personally, I don’t know what to think. Some of my relatives invest in real estate, and have run into one situation where the seller’s family members were occupying the house and insisted that they weren’t going to leave even if the place was sold. But this "mystery tenant" business is a whole other level of weird.
That’s what makes this story drift into paranormal territory. It probably is something with a normal but strange explanation, like a family member who made some sort of agreement to stay there indefinitely. Still, why all the secrecy? Why can’t the unit be shown "under any circumstances?" Is the tenant an evil wizard, or some weird old dude who has to remain in the unit to guard a portal to some other dimension? If this were a movie, it would totally be something like that.
Since the listing has been taken down, I don’t know if the house sold or if the seller just gave up. I know that I wouldn’t want to buy a house with half of it entirely unseen and occupied by a stranger, and I think most buyers feel the same way. Either that, or the seller went upstairs to try to work something out with the tenant and wound up falling through the portal to Hell.