Have the construction contract checked / by whom? Is it necessary?

Yes, of course, because some don't know what went wrong with them, others do and now want to do something about it.

That wouldn't speak in favor of the general contractor (GU). As I said, the GU also benefits when an expert keeps an eye on the subs. He also has his site manager, but four eyes see more, and above all, the site manager has to watch out for long-term relationships with the subs. If he can say, yes sorry, the expert from the client wants it that way, he can nicely pass the blame.

You believe that. You don't see all the mistakes, or you're just very lucky.

No, it's rather that you don't notice 70% at all. Of those, maybe 50% are fixed, and of those, 50% are done professionally and technically correctly. The 30% you notice are corrected with a lot of fuss so the client sees how careful the GU is. Of those, maybe 80% are professionally and technically correct – if you're lucky.

How is a layperson without expertise supposed to judge that?

That's true, but it doesn't help with any cheating later on.

Again, and sorry that I’m so brutally direct here, but with a total volume of beyond half a million and more, trying to save perhaps 4,000 EUR in expert fees already seems really stupid.
It's nice that you believe you did well with that, but you can’t seriously advise that to prospective homeowners.

I rather see all that as pessimism and overcautiousness. But surely everyone has a different attitude towards it.

I don’t think all the houses built in recent years without a building expert will suddenly show their “little problems” in the coming years.

I would also like to hear the typical problems you are talking about that a layperson wouldn’t notice or have any understanding of.

It’s usually just said easily: “I know nothing about building – it can’t be done without an expert – I don’t understand what’s being done there.”

I spent a year dealing with the topic of “building” and was practically at my building site every evening (of course, it always depends on how close you live to the site). But honestly: If you deal intensively with the subject, you can very well judge what is happening on site.

I sometimes find attitudes like that a bit strange – many things don’t add up for me.

You partly build a “cheap house” like xx...... and expect that everything is built properly, flawlessly professionally and technically perfect with some subs coming from 4 different countries.

Sure, then I need an expert.

But to me, that doesn’t fit together? If I am so picky and care so much about everything and want to have every move checked, why do I then build with partly such “crap companies”?
That’s no rarity, from how I describe it.

Therefore, once again MY advice to the OP: Just keep looking for your GU until you find the right one. It took us a long time – but it was worth it.

There is always some luck involved, no question (also with a construction supervisor), but with the right choice, you minimize your risk of construction defects.

choose the RIGHT general contractor who makes an effort, has proper trades, and supervises the construction cleanly.

How is a layperson without expertise supposed to judge that?

There are construction guides for that, I am not the only one ;-)
And besides, we have a section here called "Experiences with construction companies" (with all kinds of reviews, not least from regional general contractors). You just look up the names of your already found reliable guys with the forum search to see if they are already known (and with what findings).

About the "clean supervision" of construction sites by the general contractor, see (external) "Von Bauleitern und ... Bauleitern."

I don't think that all the houses built in recent years without a building expert will show their "little problems" in the coming years.

Freely according to Pink Panther: "the last years are not 'today'." Look here how many of the latest posts deal with attempts to soften, withdraw, and circumvent price "guarantees," and how often special attention to attempts to save on care is mentioned.

It is usually always simply said: "I have no idea about construction - without an expert it doesn’t work - I don’t understand what is being done."

This forum is also full of examples of "false rejections," where someone writes in that style: "Help!!! - tomorrow the ceiling is supposed to be installed and all the walls are ten centimeters off," and in the end, he just measured incorrectly himself. In such cases, the expert is already cheaper than canceling the cement truck and postponing all further processes.

Oh, it already starts with the foundations. Can you distinguish a floor slab that is part of the structural framework from one that is not? Would you know that it depends on whether a studded membrane under the floor slab is just still okay or not? Do you know what a statically load-bearing blinding layer must look like? Masonry, minimum cover, associated buckling protection verification, sealing in the plinth area. Perimeter insulation, capillary forces, back-ventilated or not, crack-bridging, flexible or rigid sealing slurry, application of bituminous thick coating, e.g. regarding substrate condition, connection to the window drip seal. Material compatibility of the different substances. When is a "Pfuschertasche" really botched work (i.e. a defect), and when is it still okay? Were the "OK" joints really pointed with lightweight mortar and continuously? Generally, window installation RAL conformity (three levels), which sealing tape inside and outside, design of the window sills, standards and tolerances. And it goes on like this through all trades. If you can do all this, fine, but you are not the norm. And then assuming that every client can manage that, delve into every topic to that extent, recognize any mistakes and know how it must be done correctly, or how to professionally fix a mistake—well. I claim that after one year of self-study you cannot oversee this. I now have two to three years of experience with these topics and know that I don’t know enough. Even for my next house build, I will definitely hire a building expert in addition to the project-managing architect! Then there will be a six-eyes inspection concept! That is not overcautious; it is born from painful experience. The consequential damages from such defects can be seen on horror shows on TV. Moisture damage, structurally relevant cracks, leaks, health-damaging mold, aesthetic damage from flaking plaster, etc.

The consequential damages from such defects can then be seen on horror shows on TV. Moisture damage, structurally relevant cracks, leaks, health-damaging mold, aesthetic damage caused by flaking plaster, etc.

Yes, we already had someone last week who is convinced that horror construction sites only happen to idiots :-(

That is why I can only laugh whenever I see the typical reports on YT or ZDF.

with us, with a building savings contract, all trades said, we already know, this will be inspected. In my opinion, they build more thoroughly right away, no general contractor pays double work because of botched work. Our building savings contract was very competent because it also served as a damage assessor for disputes. In the current times, an insolvency clause is doubly important in the contract, as protection for the builder.

In the current times, an insolvency clause is doubly important in the contract as protection for the builder

A completion guarantee has never been as important as it is today, yes.