Illegal construction without minimum distance to neighboring property

Do not sign, that is his problem not yours.

Otherwise, in return, allow border construction at his expense.

That was not allowed in our case.
There must be 6 m between the buildings.

(It is probably different depending on the region again)

The thing with the 3 70 m is correct.

Not necessarily. There are two ways to remedy the building violation. Either the TE assumes the setback area on her property in accordance with Art. 6, paragraph 2, BayBO, which is usually legally secured by entry in the land register. Then you would be right, and I would fully agree with the statements of . Or the TE only signs the acknowledgment of the building documents for retrospective legalization. This does not burden her own property; the TE thereby only expresses that the development to be legalized does not bother her. For the LRA, this signature then opens the possibility to grant a deviation to the neighbor according to Art. 63, BayBO. There are then no building restrictions or loss of value. Whether one is willing to do this for good neighborly relations or a handful of dollars must be weighed individually.

Since then, the seller has been trying to come over with his architect (which we do not want...

I recommend having this conversation, signing nothing, getting the documents handed over, and having the LRA explain the consequences of a signature. If you feel uneasy, politely but firmly leave the problems to those who caused them.

This signature then gives the LRA the possibility to approve a deviation for the neighbor according to Art. 63, BayBO.

If the OP were to sell and the new owners objected, would the "illegal building neighbor" still have to remove the approved constructions? And would the OP or a successor still be allowed to build something with the mentioned 3m distance from the boundary?

Better words probably cannot be found.

That’s exactly what I wanted to write just now.

...

From my point of view, the sale of the neighboring house is a good opportunity to put everything in order and comply with the applicable laws. I consider the following two options acceptable in this context: dismantling of the illegal construction or selling a part of your property to the new neighbors so that the minimum boundary distance is respected again.

How large is your property that the boundary violation does not bother you?