4 years after construction, the office also demands land acquisition tax on the house

You mean with a linked purchase I can reclaim the VAT?

No, definitely not. At least not in your case. This rare possibility exists exclusively with a property developer under special conditions. They have to sell you the land and the house together. This is not the case with you, since the seller and the general contractor are different persons or companies.
And it does not concern you as the buyer; the property developer can opt for this. You have no influence on that yourself.
Sorry, that would be nice, but it’s not possible.

One could also assume that a real estate transfer tax assessment notice from the tax office is binding. The question now is whether the tax assessment for your purchase back then is provisional or to be considered final. After all, there was a certificate of no objection to the notary and the purchase contract was legally executed and thus registered in the land register.

Therefore, the question arises whether the tax office can still change the assessment from back then and thus justify a supplementary claim. No new tax-relevant knowledge has emerged afterwards. The notarized purchase contract was also known to the tax office at that time.

This is simply regulated in the Real Estate Transfer Tax Act. Yes, the tax office is entitled to collect the tax at the conclusion of the measure, since only then is it clear how high it actually is. Before that, no assessment for the house construction can be issued at all.

No matter how you look at it, there are practically no loopholes.

No matter how you twist and turn it. There are practically no loopholes.

Yes, that is to be assumed. If nothing works in this country, collecting taxes still works perfectly. And of course, the phrase always comes immediately, ownership entails obligations. But after 4 years, such a claim could create a significant hole in the household budget.

The slump in construction also affects the FA. Outstanding payments have to be collected. o_O

In this respect, the question arises whether the tax office can still change the previous assessment and thus justify an additional claim.

I think we now have a completely normal classic developer contract, but we have already been told that additional real estate transfer tax will be incurred for special requests. (Let's see how that goes later). So the fact that additional charges are claimed if the price was not fixed from the outset sounds normal to me at first...

How does the tax office actually come to the conclusion that it was a tied sale?

If it is not stated anywhere, then they can claim a lot, but if you signed it somewhere, then you will have to pay 100%

How does the tax office actually come to the conclusion that it was a tied deal? If it is not stated anywhere, they can claim a lot, but if you signed it somewhere, then you will 100% have to pay

Did you even read the thread? That is stated in the purchase contract that the OP concluded. Purchase of land with the simultaneous obligation to build a semi-detached house with the general contractor XY. The tax office cannot get information any easier than from the submitted purchase contract, which was even notarized.