Parkett joints installed untidily? Defect or tolerance?

Has it already been sanded and oiled or is it still in untreated original condition?

It should actually already be sealed, according to the publisher.

So it really looks like someone has lived in it for a while... not like it’s new...

Under these circumstances, I will definitely demand rectification first, if that is possible!

One has to do that – even though I don’t believe that the result could be free of defects afterwards. But an expert sees that more clearly.

It really looks like someone has been living in there for a while...

Vandals don’t "live," vandals squat.

It is oak mosaic parquet, solid, 8 mm, glued - from the company Bembé.

Then the question is which wood quality was agreed upon... Removing this parquet again is a huge effort and would likely be disproportionate. Sanding and resealing should work, and in the process, the joints can also be closed. It is still very annoying because, on the one hand, it is unnecessary since it could have been avoided from the start, and on the other hand, 8 mm is not a lot, so every sanding somehow hurts. Still, the parquet will last you a lifetime, as you usually only sand it every 25 years rather than every 10.

What I noticed about your picture: the baseboard is sagging quite a bit, the floor is not even. There is a very large gap visible.

Removing this parquet again is a huge effort and would probably be disproportionate.

On the other hand, it is absolutely equally disproportionate to have branded goods processed by an unqualified person. In my opinion, the goods have visibly suffered; edges look bruised like "stonewashed". Sanding, which would ultimately have to work down to scratch-deep, borders on "surface milling" and the result plays a horror movie in my mind when I imagine it being done again by the same foolish hands. To what extent the correction should be "initially" accepted here, I cannot assess from a consumer law perspective, but I do not expect a satisfactory result. I would wish for a precedent-setting judgment against processing high-quality goods by unskilled or semi-skilled workers, as it is becoming an epidemic: cases of branded clinker bricks laid by semi-skilled stone setters and grouted by "Estrich-Achmeds" (Thanks for this nice term) are relatively regularly displayed here; currently, this week in another thread it is about windows from a brand manufacturer that were improperly assembled and "installed"—which also seems to be in fashion. Misusing a branded product in its construction service description to create the appearance of a quality level and then botching it during processing (we remember from math class: a product is bad even if only one of its factors is bad) must finally be freed from the aura of a "petty offense"!