Advance payment for the window installment

That’s how our general contractor explained it to us, just like @11ant wrote here. He said the payment for that had to be processed proforma through him, but he would pass it on 1:1 to his electrician (which is basically none of my business), because we have the construction contract with him, not with the electrician. Roughly speaking, if I pay the electrician for 20 extra sockets, and then one breaks, the electrician can say "that was one from the GC", and vice versa? He actually said it was for warranty reasons, and because we are his customers with the house.

On the contrary: if the GC could be bypassed, his lawyer would tell him in case of a complaint that he could calmly declare himself not responsible. The electrical trade was either removed from the GC’s scope of services or would be deemed tacitly accepted at the moment you let your craftsman onto his work. Whether it is the same craftsman is irrelevant. What counts is whether he acts as an agent of the GC or as an independent contractor. For the electrician, this would mean that he would then provide warranty for ALL sockets directly to you; the keyword “upcoming trade” has been mentioned here several times—mostly in threads about self-procured washbasins.

It was different with the photovoltaic system. We commissioned that afterwards, directly with the electrician; there is nothing about that in the house contract and the electrician bills me himself. But here again, I made sure that the GC knows about it and is okay with them installing a photovoltaic system on "his" house. We haven’t accepted it yet.

Legally, that’s not really different, although in this special case it is more clearly delineated. But even here, the roofer (or the GC regarding the roofing trade) could construct a tacit acceptance.

Since "my" craftsman has been Heinz von Heiden’s partner for decades, they work well together, so there should be no problems. Since Heinz von Heiden allows these upgrades, they still have a certain responsibility and owe me a flawless overall building anyway. It might be different with external craftsmen who have nothing to do with Heinz von Heiden. But even then, the Heinz von Heiden site manager can help and act as a mediator. You just have to be optimistic.

Please do not lead possibly naive readers into such unfounded optimism. The GC only owes you his overall work to the extent that you have not reduced his scope of services. Conversely, you might also owe him the profit from trades that you awarded as upgrades with his tacit consent. Identity of persons of third parties, as said, does not fundamentally change that. How often do I have to say that the average private homeowner never operates on equal footing with the legal departments of the big names?

Yes, we asked the general contractor (GU) to offer such a guarantee only for this early payment, but they are not interested in doing so. From their point of view, this was just a friendly offer that one can accept or reject.

That would also be complete nonsense: a completion guarantee serves to secure the completion of the overall work by the GU; the GU is not responsible for Hermes guarantees regarding its subcontractors.

How far away from the windows are you currently: foundation earth electrode, ring beam, ... ?

That would also be complete nonsense: a completion bond serves to secure the completion of the overall work by the general contractor (GU); the GU is not responsible for Hermes bonds regarding its subcontractors.

I have not applied for a completion bond. I understood this statement to mean that it is only possible to obtain a guarantee for this advance payment.

You can certainly make an advance payment to secure a discount. But only and really only with a direct bank guarantee. If the manufacturer or the GU goes bankrupt, which can sometimes happen very quickly, then the bank is liable. If a bank guarantee is refused, then something is fishy.

How far from the windows are you actually currently: foundation earth electrode, ring beam, ...?

We are still in the demolition/earthworks phase. It will take several more months until the shell is finished and the windows are ordered.