Parquet with many small holes (woodworm) installed

such hole-like appearances are neither mentioned as acceptable in the regulations, nor are they acceptable for aesthetic reasons.

That means you consider the data sheet invalid / ineffective in terms of its effect as an agreement of quality, and although the customers "bought despite reading" and thereby tacitly accepted it, they could (because it is contrary to the norm) claim it as a defect?

Whether an agreement is permissible or impermissible is for lawyers to decide. That is a legal question! However, it is correct that - insofar as a product data sheet was handed over before purchase - these hole-like appearances characterize the product. It is thus inevitably also correct that the end consumer accepted the conditions. And that in turn means that an intended complaint about defects will be futile, must be futile. Therefore my advice: save your energy and apply it specifically where success can be expected. And that is, if you commission it yourself, the removal of the features by means of a hard wax matched in color to the parquet surface. That should answer the question from "11ant"?

A layman actually has no chance to discover that in the exhibition. The seller says not a word about it and the buyer has entirely different problems: wife nagging, child crying, prices, etc. There are only sample areas without wormholes there. Most people probably don’t even know that such a thing exists.

The OP likes it anyway

Yes. But that is not the seller’s problem if the children whine or the wife is annoying.

It is rather an expression of a certain naivety.
Sometimes one gets the feeling that choosing a razor or toothbrush causes the interested party more research effort than the parquet floor costing many thousands of euros.

And I don’t want to exclude myself from that. In my shower there are floor tiles that could well have an R-class one level higher.
But I only became aware of it when I tiled the utility room with R10. In the shower there is R9...

In my shower there are floor tiles that could definitely be a class R higher.

Please forgive me: Tiles with a specified R group have no place in wet areas. R groups apply to work areas where slipping hazards due to floor contaminants are to be expected. Here, the test surface is also walked on with work shoes (which is rather unusual in showers). For showers and swimming pools, the requirements for "wet barefoot areas" apply. Regulated in the relevant leaflet of the statutory accident insurance. And there we find under item 2.1 Slip resistance the evaluation groups A to C. Ceramic tiles and slabs in showers fall under evaluation group A (and not R9 or others). Sorry, but this info only as a side note.

Good to know, because both tilers and tile consultants as well as a good acquaintance, who happens to be a tiler, always talk about R-classes. But it doesn’t change the result. I didn’t do any research, relied on advice, and now the shower is quite slippery.

But that’s my problem, I had the tiles in my own hands.

That means you consider the data sheet, in terms of its effect as an agreement of a quality, as inadmissible / not effective, and although the customers have "bought despite reading" and tacitly accepted it, they could (because it is non-compliant) claim it as a defect?

Whether an agreement is permissible or impermissible should be decided by lawyers. That is a legal question after all!

I must admit, given the data sheet, I wonder how low we have already sunk? Wormholes in the parquet – did that exist 20 years ago as well? In my family, we work a lot with wood, and I was raised with the awareness that wormwood is waste. The professional removal of such holes was at most an issue with existing furniture (or roofs), where a little creature had freshly nested. But that it is now offered from the outset shows me that for many, quality no longer matters. I somehow also see this as a disregard for the work of the craftsmen. No matter how perfectly they work, it remains shoddy workmanship.

Whether the matter is legal would probably also be a question of price in the end. However, I can hardly imagine that anyone could get more than professional removal out of it. What would one want to sue for here? Poor advice? No one was deceived, nothing was fraudulently concealed, and presumably it is also still reasonable within the scope of common practice. I can't think of anything.