How is the valuation of banks / financiers conducted?

Purchase price = value used for the loan. However, it is not the same as what the bank determines as an internal value ... purely for determining conditions. Only the renovation is handled differently. Some only count 50%, some 100%, others again deduct own labor. Just tell me what the house costs, renovation, own labor, and whether there are offers for renovation

The house costs 409,000. We have not obtained any offers. It is only about finishing the flooring work in the basement, painting, and installing new floors in the children's rooms. We are doing all of this ourselves.

I was just surprised that with the same provider, a difference of 70,000€ was determined in the value within one day.

Then there was an error the first time (or the second time?). If nothing has changed in the data, the difference is quite large. Maybe the colleague just needed an argument to give you a better condition :p

Estimated the first time, calculated the second time...

427k to 363k is exactly a 15% depreciation. But now I'm surprised that you are buying for 409k and 427k comes out. Are 18k the self-performed work on the floors etc.? Otherwise, free yourself from bank values. You will never really get the true value in the banking system anyway. I would be more interested in the conditions. Have you approached several banks? To put it bluntly, Bank A can give you the feeling that your house is worth more but finance you worse in terms of interest.

No, the equity contributions are not that high. We would estimate them at around €10,000k. We have obtained several offers and are currently waiting for the remaining offers. Currently, we are at approximately 1.7% for 15 years. The Allianz would go down to 1.5 with a higher income proof of €81,000 p.a.