Broker sells house without current building permit. Notary costs?

Fraudulent misrepresentation is that.

Basically, the client always pays. In this case, that is the broker
Unless you have given him written permission to "order" on your behalf.

If you are upset about the behavior and want to do something good for the new buyer, then send the seller a registered letter with delivery by a bailiff (does not cost 20 euros) with your finding that, according to your research, the building permit would be invalid. If he still sells, this is well documented, and the buyer could then easily challenge the purchase due to fraudulent misrepresentation.

Fraudulent deception that is.

Basically, the orderer always pays. In this case, that is the broker
Unless you have given him written permission to "order" on your behalf.

At most, if you interpret the emails that way. But there is no signature or anything similar

What was the wording of the email?

As stated right at the beginning, "Call the notary" and explain to him or his notary inspector, who probably also wrote the contract, what happened. Whether you will even receive a bill is questionable. BTW notaries are obliged to remain neutral and must not notarize if they are aware of discrepancies. That means for the next sales attempt, the realtor will need a different notary.

Realtors are criminals or good-for-nothings 99% of the time. It is and remains an unserious business. Probably the case again here.

Under no circumstances pay anything, that much I can advise you.