How is the terrace area calculated?

If you are so smart, why are you asking here? Rarely seen such an attitude here.

Rather unbelievable that you don’t see a problem when a seller simply states 20 square meters too few, and that you’re even being attacked here, told to just not make such a fuss about it.

Then that probably applies to lawns too, you smarty-pants

Nanana, you’re the smarty-pants right now. Because it doesn’t matter at all when buying!

namely if 170sqm is stated in the exposé

But it won’t be stated there. The purchase contract is a contract drawn up by a notary. The exposé is nothing more than an advertising sheet or brochure with compiled key data, either from the owner, the heir, or an authorized representative, which can also be a real estate agent. An exposé is meant to make you curious.
The real estate agent’s terms and conditions also include a note that they do not guarantee accuracy; this is called a disclaimer of liability. After all, the agent earns money differently than by measuring the house.
And yes, it’s up to you to convince yourself of the quality of the house. Either you want it, flaws and all. If you don’t want it, surely someone else will.
An exposé will never be the basis of a notary contract. The basis for the notary is the land register. And that is not illustrated but soberly in black and white and only contains one piece of house… sorry… residential building on such-and-such a plot, what has been authorized. You can trust that. And if an owner adds or removes terraces, that has nothing to do with the land register.
If a real estate agent talks about a park-like property, that will never appear in a notary contract, nor play any role. And you will have no right to a park-like property.

No, of course it matters if the seller deceives you fraudulently

First, google yourself what fraud and deception are. Then think about what fraudulent deception is. You are quite far from that here.

I don't even know where the drama is; if the information is incorrect, it can also be challenged after the contract is concluded.

Hard to believe that you don’t see a problem when a seller just states 20 square meters too few and that you even get scolded here, being told to just not make such a fuss about it.

If that’s the case, then be happy.

I suspect you are a bit upset and that’s why you write so many unobjective posts. Count slowly to ten. That should help.
If I want the house, there are two options. 1. You negotiate the price down with whatever arguments you like. 2. You make a contract and sue for the reduced costs afterwards.

Your argument may be correct. With a real error of over 10% you can indeed have a dispute.

How is the terrace calculated, with 25 or even 50%?

Nanana, you’re quite the smart aleck right now. Because it doesn’t matter at all when buying!

But it won’t say that there. The purchase contract is a contract drawn up by a notary. The exposé is nothing more than an advertising sheet or brochure with compiled key data, either from the owner, the heir, or an authorized person, which can also be a real estate agent. An exposé is meant to make you curious. The agent also includes in their GTC a note that they do not guarantee accuracy, which is called a disclaimer. After all, that’s not how they make their money, by measuring the house. And yes, it’s up to you to convince yourself of the quality of the house. Either you want it or you don’t, with all its defects. If you don’t want it, someone else surely will. An exposé will never be the basis of a notary contract. The basis for the notary is the land register. And that is not illustrated, but soberly in black and white and contains only a piece of house... sorry... residential building on such and such a plot, what was approved. You can safely believe that. And if an owner adds or removes further terraces, that has nothing to do with the land register. If an agent speaks of a park-like property, that will never appear in a notary contract, nor will it play a role. And you will have no right to a park-like property.

First, google yourself what deceit is and what fraud means. Then consider what fraudulent misrepresentation is. You’re very far from that here.

What a (long-winded) nonsense. There are numerous BGH rulings on false information in exposés. You don’t even know how it’s regulated here!

If the actual living area deviates by more than ten percent, this constitutes a material defect. The consequence: The buyer has a claim for repayment and can, if applicable, withdraw from the purchase, demand a partial refund, or request a reduction of the purchase price. The exact size must be recorded in the purchase contract, as only this contractual agreement counts. In short: The seller is usually liable for the accuracy of the living area specification and should therefore be sure that it is correct.