300 m², hillside location, built in 1963, buy or not?

I also don't believe that the price is negotiable in this range.

I think so too, because the price corresponds roughly to 20 years of heating costs. Whoever has the financial means to maintain such a property does not mind it either. Whoever sells something like this must have endurance – and a suitable broker for it. The purchase price is already a "bargain" – like a Rolls Royce Silver Spirit that you can buy for €20,000 with low mileage, original patina, and without major investment backlog.

I also don’t believe the price is negotiable to that extent. The sellers don’t seem to have a problem leaving the house unused for almost two years.

Make an offer of 350k here with a good reason. Hit or miss. Such a property is hardly sellable. Perhaps the agent hasn’t received a suitable or any offer yet. That wouldn’t surprise me.

I hardly ever write here, usually just quietly read along (thanks for the interesting posts by the way), but the place is amazing... A Mid Century dream.... damn, the hallway... and the spiral staircase. Awesome! If I had the money to spend X thousand euros a year on heating, I would leave the floors and every usable wall paneling/wall tile exactly as they are. Restoration instead of renovation... I would have fallen for that house too.

Edit: Except for the kitchen, and living room and a few of the rugs ;-)

What is the reason for the sale? Have you already viewed the piece of jewelry?

Make an offer of 350k here with a good reason.

You can always try.
The prerequisite for negotiating is that you actually buy afterwards – and the decision is still pending.
I find time-wasters who negotiate a price and then say "I'll think about it" disgusting.

Restoration instead of renovation... I would have been weak for that house too.

Yes, that would also be my way.
Technical modernization only while preserving the character of the property.

Just use common sense. 300 sqm floor at €50 + installation costs, adhesive, baseboards, etc. So what price do you get? Already €15k without removing old tiles, installation, and especially without all walls and ceilings. I would guess the painter (removing all coverings, filling, possibly sanding, new covering/painting) would also charge another €40-60k.

He wants to do that himself. And if you look at the pictures, not all floors need to be done. There's beautiful parquet, why should that be renewed? What I would NEVER do with the property is take the swimming pool out of operation. That’s THE highlight of the house. I can't say anything about the remaining costs.