Notarial Purchase Agreement - No Guarantee for Building Land

Ouch. So the problem is not that the location of the property being within the scope of the development plan is questionable. Nor is there a dividing line visible that separates bungalow plots from high-rise plots, and you are not restricted to a specific house model. "Only" (but not to be underestimated) the seller wants to sell the property "old parcel number," and by acquiring it, you would assume the position of the reallocation creditor. ...

Almost, but not quite:

1. The development plan dates from 1985 and includes parcels with different designations, which are only separated by a dashed line on the development plan. The dashed line corresponds to: "proposal for parcel division."

2. We are now acquiring a property with a parcel number that does not appear as such on the map in the development plan. The property, due to its surroundings (roads, green spaces directly adjacent, etc.), is clearly assignable to the development plan. However, the proposed division mentioned in 1. has been slightly changed.

3. According to the building authority, there is no more recent version of the development plan, and the responsible person was also able to identify the property based on the surroundings and features on the development plan.

4. The seller also refers to the development plan and sells the land as building land. However, he does not want to assume liability in the purchase contract for the correctness of the development plan nor provide a guarantee that it is actually building land.

5. The notary clerk informed us about point 4 and described it as unusual that a seller demands building land prices but does not want to contractually sell it as building land with a guarantee.

My issue, therefore, is more: Is it really unusual for a sale not to assume a guarantee that it really is building land?

I think: If I demand building land prices, then I also confirm and assure with liability that it is building land. This is not about specific building preferences but generally about whether it is buildable or not.

(Since this is not about the interpretation of whether the property is really within the development plan and the internet forgets nothing, I am not sharing the plans.)

You are currently constructing totally nonsensical possibilities. But you know that yourselves.

No, not at all. I would rather consider you careless. We ourselves have bought and sold several properties under the condition of a positive preliminary decision. Whether this is necessary in this case is best asked from a building expert as a layperson.

and sells the land as building land

He advertised it as building land. What does the notarized contract say?

My topic is rather: Is it really unusual that a sale does not guarantee that it is really building land?

Yes. I have been working at a real estate bank for 30 years and have seen more than enough contracts. I have written what is usual.

We ourselves have bought and sold several plots under the condition of a positive preliminary decision

Who is stopping the OP from submitting a preliminary inquiry with the content "is it possible to build a single-family house on the plot according to the specifications of the development plan"?
His question is quite different from your situation.

I think to myself: If I demand building land prices, then I also confirm and guarantee, with liability, that it is building land. This is not about specific building wishes, but about whether it is generally buildable yes/no.

If you want a guarantee, conclude the contract under the condition of a positive preliminary decision. However, you must then request this yourself in a timely manner. We also set deadlines for this back then.
Is this common? I would say: I don’t know any house builder who hasn’t informed himself 100% whether the land is really buildable before buying it. Possibly a short phone call with the city building authority is enough.

4. The seller also refers to the development plan and sells the land as building land. However, he does not want to assume any liability in the purchase contract for the accuracy of the development plan nor any guarantee that it is really building land.

The guarantee is provided by the development plan itself (once it has become legally binding). All areas that are not otherwise designated (e.g. traffic areas including parking spaces, green strips, retention basins) are building land and can be developed according to the applicable usage template, period.

(Since it is not about the interpretation of whether the property is really included in the development plan and the internet forgets nothing, I do not share the plans.)

Then I do not understand the problem or there is none. If it is undisputed that according to the development plan the property is building land, then it does not suddenly lose this status because its seller refuses to give a guarantee. Just buy the property and then submit your building application. If the legally binding development plan is to be changed afterwards, you are affected and could raise objections against the change. But as Mr. Klaus from MA2412, who is usually well informed, assured me, this is not planned.