The outside photos of the house, look very nice.
And that's where the positivity ends for me. Pardon my skepticism, BUT:
Seller: I want to be there for all showings.
Seller: Because of the uniqueness of this property.
Buyer: Oh, ok.
Is that a good reason that the seller needs to be there? Uniqueness? I'm thinking no. The house has been empty for four years, so there's no personal stuff there to neb through. My opinion: The seller doesn't want the buyer to look at certain things too closely. If buyer starts getting too close to the closet of skeletons, they'll be shooed and encouraged to go look at something else. As a buyer, I know I would not want the owner following me around, I would want to inspect things pressure-free.
2. $400K sounds like a LOT for a house that needs so many significant repairs. Holding tank damage, broken solar with panels that surely need replaced considering the age of the existing panels. Technologywise, I mean, those panels (and there are just a few of them!) are probably less than 100 watts each.
3. The septic has NEVER been pumped?
4. Crummy access road to the house. May be a coincidence, but it sounds like as soon as buyer started looking at the house, neighbor #1 built a fence across their access road, keeping the buyer out. And neighbor #2 said buyer can use their access road 'occasionally'. Ugh. I translate that as 'I don't want you to use my driveway, but I'll sound mean if I give you a flat out No'. So, buyer is stuck with a crummy access road ... no, buyer will need to improve it, buyer just got stuck on it!
5. Just the fact that so many things need fixed that the buyer has to take care of, is a dealbreaker for me. I've sold houses before, I always fixed things BEFORE listing them for sale. Isn't that the way it's supposed to work?
EDIT: Oh, I see you just said you passed on it. Yay! Excellent decision. That house is a money pit. And the neighbors don't sound friendly. Sheez, look at me, I'm still trying to talk you out of it.