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

I looked it up. Even if the proceedings have been opened and the debtor performs without knowing about the proceedings, the performance is valid. When in doubt, have them sign that no insolvency proceedings are pending. Then you are out at the latest.

Too fast.. So no publication and confirmation by signature and you're out.

Get a commercial register excerpt on the day of the transfer (also available online): as long as the guy is still managing director and no insolvency proceedings have been opened against his GmbH, then cash against receipt is okay. Otherwise not!

Get a commercial register extract on the day of the handover (also available online): as long as the guy is still managing director and no insolvency proceedings have been opened against his GmbH, then cash against receipt is okay. Otherwise not!

The fact is, both the main office and the branch office no longer exist, you can go there ..... he has not deregistered/changed registration, although he has to .... a bit confusing, or does it not matter as long as no insolvency proceedings have been opened?

you have a contract and a monetary debt vs. a GmbH. If the guy is still their managing director and the GmbH is not insolvent, you can give him the money in cash. Pay attention to the Handelsregister-B of the contract and the extract from the register, these must match

The fact is, both the main office and the secondary office no longer exist, you can go there..... he has not deregistered/registered it, although he has to.... a bit confusing, or does it not matter as long as no insolvency proceedings have been opened?

You are already doing more than what is reasonable to expect from an ordinary person. You would basically have to start with every large amount and check whether the company is in insolvency proceedings. I also don't think you want to avoid a double payment, but rather "get back at him" by transferring his money to the seized account so he no longer has access to it. Maybe understandable, but contracts must be honored. Withhold an appropriate amount for defects or non-completion and pay the man. You are making yourself crazy here over (presumed) desires for revenge. That won't get you anywhere.

You are already doing more than what can be expected from a normal person. Basically, you would have to start with every large amount and check if the company is undergoing insolvency proceedings. I also don’t think you want to avoid a double payment, but rather "get back at" someone by transferring his money to the seized account so he no longer has access to it. Maybe understandable, but contracts must be adhered to.

With defects or non-completion, retain a reasonable amount and pay the man. You are getting worked up here because of (presumed) revenge motives. That won’t get you anywhere.

When the kitchen was being assembled, I offered drinks etc., helped out, and disposed of the rubbish.

Then he showed his true colors again:
- He moved the kitchen island so that the distances on the left and right were different. His statement: "I informed you back then that the outlet for the downdraft extractor was changed by the screed layers."
That was not the case; when he came to measure, he said everything was fine. I can live with it, but again he shifts the blame to others.

The kicker was that during measurement, he did not take into account the handle of the patio door, so the refrigerator does not open a full 90°. He told me this, and I said, "That’s fine with me, but my wife has to decide!!!"
My wife came the next day and told him immediately on site. He then got offended, moved it, and continued his work.
We could have chosen another handle, but that alone would have cost us about €800 (flat handle plus installation), which we did not see as reasonable.
At the final inspection, I saw that he had charged 4.5 hours for this (additional service) and wanted to charge for the trim strip as well.

Me: What is this supposed to be?!
He: Yes, your wife wanted us to move the whole thing.
Me: Yes, because the handle was in the way, or do you want to pay for the new handle?!
He: When I was here before measuring, the handle wasn’t on.
Me: Oh really? Then take a look at the photo; here you can see that the handle was already installed by you before measuring.
He suddenly ignored it and said: Yes, but I only checked if the sockets fit.
Me (just laughed): You made a mistake, period... I won’t pay a cent for that.

Yesterday, the stonemason pointed out the silicone work by the kitchen installer to me. I spoke to him about it, and he said that this can happen with silicone because it can settle...