Existing property or construction financeable?

Make an offer, enclose financing confirmation. If not, then not, if yes, then good. If they really come back to you again in your case, I would immediately go down by another €20,000.

If they really come back to you again in your case, I would immediately drop another €20,000.

Yes, that's what I thought too

plus €46,000 purchase incidental costs [..] deductible equity €30,000 [..] €25,000 subordinated loan

That somehow doesn’t add up. I only see €16,000 as subordinated loan. Ok, the house didn’t work out now, you already declined. But for other existing properties, you should also factor in renovation costs, kitchen, etc. In general, your income is more than sufficient for all kinds of real estate. Especially if 100m² of living space is enough for you, you should be able to find something.

I was mistaken, it was a €405K loan. The bank is only financing €380K, the rest is subordinated.

Of course, we took incidental costs into account. There was a fitted kitchen included, and we would have only needed to repaint and lay laminate ourselves. We could have easily managed that with €3K.
Of course, each house needs to be reassessed to determine how much is still necessary.

The subordinated loan is just an extremely expensive substitute for equity.

I also had an offer where such a thing was included - allegedly the interest on the main loan would have become so much cheaper that it would have been worthwhile.

You actually don’t even have the incidental costs of the purchase available, and for a financing of over 100%, the other conditions were not even that bad. If the house is a very good fit, and there are not many alternatives, then really make an offer to the owners. What do you have to lose?

The interest rate on the main loan was over 2% (instead of 1.4% from the previous banks).

The house is not worth it to me at that price (additional interest costs). And these 18,000€ for the real estate agent just make me angry now for such poor service (doesn't know which walls are load-bearing, material of the walls, can't read the building description, and tells the expert that these are definitely double-glazed windows, although they are triple-glazed - as stated in the documents) I am not willing to pay that. In the future, I will not consider any houses with 4.73%. A house without an agent is difficult here, but it really doesn't have to be that much...
There will also be other nice houses coming on the market or we will build one ourselves.
Your assessments show that we basically have a chance.