Damp basement wall?

I know it this way, that with real estate one always writes a defect formally in writing with a deadline by registered mail. All emails with first and last names as sender also end up in my spam. Friends contact me via WhatsApp. I would possibly discuss everything else with via private message. However, he has to contact you.

He can gladly do that :)

I think our buyer wants to feel out what is possible first, something like that, which is why by email. There is no concrete demand in there.
We will take the time and contact a lawyer to clarify things right away and avoid making mistakes.
Thanks for the suggestions in this direction.

Normal lawyer or not respond at all and let him bark. Sometimes I don’t answer emails for days

I wouldn't react to that. The risk that a lawyer is already leading things behind the scenes seems relatively high to me. Following the motto: collecting written statements from you, setting traps, etc., from which something can later be constructed. Because if a letter from a lawyer came to you immediately, the risk would be too great that you would also run to a lawyer right away and no longer make any unconsidered statements.

The fact is, he wants money. So he won't be satisfied with any justification from you anyway. Immediately put his cell number on the block list on your phone, etc.

Time is on your side, because an expert appointed later in the conflict will always find it harder to determine whether the moisture damage became visible before or after the purchase and note that in the report accordingly.

So long story short: don't respond to emails, reject calls, always answer with a false name when the number is hidden/unknown, and wait for the other's reaction. If a proper letter with a demand and deadline arrives, go to a lawyer.

...what kind of construction expert was that anyway? That's the first thing you look for: moisture damage in the basement and ground floor, that's the ultimate negotiation opener. You just have to move a cabinet for that.

Thank you very much for the hints. We will arrange an appointment with the lawyer at the beginning of the week and then we will see further. For now, we will not react.

I really wouldn't have seen it that bad, you opened my eyes!

If an expert was present during the purchase of the property and did not detect the current moisture, either the expert is to be criticized or the defect occurred after the purchase. According to the 2nd picture, the wall is in good condition. Moisture is only visible in the corner. A moisture measurement should be carried out in the entire basement area to prove this condition. Only the 2nd picture indicates a defective downpipe in the exterior area.
Best regards