Property purchase - Risk of a "linked transaction"?

As the colleague has already noted several times, the tax office interprets a divided plot and multiple houses built with a construction company as a tied transaction.

as colleague @11ant has already pointed out several times, the tax office interprets a divided plot and multiple houses built with a construction company as a tied transaction

That was not the case with us. The real estate agent sold the houses of the general contractor; at the notary appointment, all builders met who purchased their plots from one property, the plots were divided, and one part of the plot was designated as a WEG for access. The general contractor and the real estate agent were only involved with the planning and buildability and organized everything.

We received exactly such an offer back then. Purchase of land from a GbR plus a simultaneous preliminary contract for the house construction. We were promised the moon and stars, that this was always done this way, had never caused any problems, etc. But the tax office is not full of fools. If they classify it as a linked transaction, you’re in a bad spot. I do not doubt that some builders have gotten away with it, but even if everything really did go smoothly every time, you could still be the first one to run into problems. Or unpleasant mail might arrive afterwards... It was too risky for us.

No developer obligation on the property and no economic ties between the property owner and the prefab house company sound good at first. But you sound like a believer in the myth that building with a prefab house company is faster. You can submit a preliminary building inquiry yourself, even without demonstrably being a prospective owner. One small difficulty is that the property does not really exist yet (with regard to the exact location, area size, neighbor distances). Is there already a development plan for the area? Securing the planning preliminary cost risk is legitimate, but a preliminary contract is a means your lawyer will advise you against.

The sale of the property is to be handled through a GbR, i.e., since, as mentioned above, it involves several properties, they will be jointly purchased by the buyers and later divided accordingly.

The seller should parcel the property himself, before selling it (when he marks it out by surveying is another question). The GbR solution is not only an unnecessary complication from a processing point of view in my opinion. I also wouldn’t want to spoil my credit rating by entering into a joint partnership with my future neighbors (even if they were all my classmates and confirmation mates and still serve with me at the fire department, no). The devil's bargains that some people are willing to make when a chance to acquire building land beckons sometimes take quite questionable forms. The desire to build clouds judgement. By the way, I would also not want to be allotted the long parcel at the back left as dissolution assets from a property company if I preferred the crosswise one at the front right.
So I do not see the feared tying transaction as described before, but rather a few small yellow warning lights about the procedure, and you are still in need of demythologizing. Those who are naive get eaten.

To my understanding, the landowner originally contacted the sales manager/prefabricated house company himself, since several still undeveloped plots are to be sold and the sales manager is also coordinating the development to some extent.

Excerpt from Juraforum: The development of a plot is according to § 123 of the Building Code the responsibility of the respective municipality, whereby it should be noted that according to § 123 para. 3 of the Building Code there is no legal entitlement to development, even if a development plan provides for the development.

I’m curious to see what will happen in your case.

If you have the plot number, you can already inquire at the building authority of the municipality whether the plot is developed and if not, whether there is any information on how long it "might" take.
They are very friendly if the potential future builder asks beforehand and they are not faced with a fait accompli.

At the same time, you can clarify whether your desired house, e.g. a townhouse with two full floors and a hipped roof, may be built or only a 1.5-story gable roof house with maybe dormers are permitted.

Whether you are allowed to set up your garden house at the back of the garden or only directly at the house, and such things that are of great interest when building a house.
For example, whether you may only plant an 80 cm hedge around the house and if you don’t want to spend your life on display, whether you have to stay away from the visibility protection at the property boundary.

Then you might even be able to save yourselves all the planners.

Anyone can make a preliminary building inquiry; you don’t have to be a landowner for that.
Sounds somehow like someone has farmland and dreams of getting rich by selling building plots. And the buyers shall pay for the feasibility.

Excerpt from Juriforum: The development of a property is according to § 123 Baugesetzbuch the task of the respective municipality, whereby it should be noted that according to § 123 para. 3 Baugesetzbuch there is no legal entitlement to development, even if a development plan provides for the development.

This does not exclude the possibility that there is a huge property in an otherwise developed building area, which would in itself be divisible to such an extent that a cul-de-sac to its half dozen parcels after division would make sense, but which is currently not yet considered in any municipal plan.