Kitchen seller wants the remaining payment in cash, does not want a transfer

So it's just about "revenge". NO ONE is protected by this, the OP simply acts in breach of contract if he transfers the money. From a human point of view, each individual point may even be understandable. Legally, however, the OP must comply with the contract. For the removal of defects, of course, a reasonable amount can be withheld. The rest must be paid. And in cash. Provided there is no entry regarding insolvency or impending insolvency in the public announcements.

Thanks, but a question out of curiosity:
Breach of contract or not, why should a craftsman insist on being paid in cash instead of receiving a transfer?

Why do you only sign it when you then have problems with it?

Only cash is real!

Or because he may be acting in a "tax-optimizing" way. Or because he wants to outsmart creditors.

Otherwise, banknotes denominated in euros in Germany are the only legal means of debt settlement. Unrestricted! Transfers, Bitcoin, gold, or other currencies are only possible if both parties agree.

Note: Giral money is not cash, but merely a promise of the legal means of debt settlement. Ask the holders of Cypriot bank accounts from 5 years ago, they know the difference.

Thank you, but a question out of curiosity: Breach of contract or not, why should a craftsman insist on being paid in cash instead of receiving a bank transfer?