Pre-made purchase contract - special services?

Yes, but it's about the value of the house: do I already include special equipment worth 20,000 in the purchase contract or do I select that later. I don't see any fraud in that.

The problem here is that there are indeed tax authorities that query subsequent special requests from project developers; but you have already paid VAT on these, and the tax authority would like to still collect the proportional real estate transfer tax (especially if these were invoiced by the project developer themselves).

No, it's not fraud; just tax evasion.

2) Consideration also includes

[*]1.
Services that the purchaser of the property grants to the seller in addition to the consideration agreed upon in the acquisition process;

And in the end you pay twice; since VAT and real estate transfer tax were then due.

Yes, but it's about the value of the house: do I already include extra features worth 20,000 in the purchase contract or do I only specify them later. I don't see any fraud in that.

No, it's not. The question is only on what the tax office's calculation is based: If it's on the purchase contract (without the additions in the specification), then that's obviously good. But what if the tax office wants to see the invoice or raises a reservation? I don't know the procedure. And it probably isn't handled exactly the same everywhere.

We have now fortunately been able to buy a property free of developers, but beforehand we also viewed many such properties. It was always said, "this is a separate transaction, you do not have to 'officially' build with company xyz, contracts are then spaced far enough apart in time."

We were fortunately able to buy a plot free of any developer now, but before that, we also viewed many such plots. It was always said, "this is a separate transaction, you do not 'officially' have to build with company xyz, contracts are then timed far enough apart"

Well: Ultimately, the tax office will judge that. The application of the law tends more towards "it's actually a linked transaction." Even some adventurous company structures don't help there. The tax office isn’t stupid either. And the seller can say a lot..... he’s not the one who pays the bill.

The easiest thing, of course, is simply to buy a plot – without any obligations.