Land with construction obligation = + 20% market value!

The "transaction value" is certainly meant, which serves as the basis for the notary's fees. Often, the transaction value is the purchase price, but in this case, the construction obligation is simply taken into account as increasing the transaction value.

AFAIK, a construction obligation does not have to be notarized. So, a few euros could have been saved if the construction obligation had been agreed upon separately in a contract (without a notary). Now, the only option is to pay the bill.

The amount increased by 20% refers to the business value according to §§47,97,36.

The property was sold on behalf of the city, which is also why there is the construction obligation! I do not believe there is any room for negotiation regarding the contract.

I don't believe there is any room for negotiation regarding the contract.

Not anymore, after the signature at the notary, that is clear. Other future property buyers who happen to read here can suggest to the seller (= the municipality/city) for future transactions to regulate the building obligation differently -- without a notary. Whether they will be successful is another matter entirely.