Is the window installation correct? Is it wind-driven rainproof?

An expert does not provide a solution because they do not do execution planning; they only point out defects.

To me, it rather reads as if the client saved money in the wrong place. I would not be surprised if there is no execution planning at all and the site manager is possibly a "skilled worker" from perhaps the general contractor.

Sorry, of course that is the famous crystal ball. But such a thing does not exist when qualified specialists are on site. Especially since this applies to the entire building and not just to a trade where botching is done.

An expert does not provide a solution

So far, I have experienced that the expert tells me what is wrong and how it should be correct.

Both are correct:

So far, I have experienced that the expert tells me what is wrong and how it should be correct.

I know it that way too – from YouTube videos by experts.

An expert does not present a solution, because they do not do execution planning; they only point out defects.

This means that the expert behaves differently in real life than on a video channel, and pays attention to the tightrope walk between expert (only complaining "destructively") and planner (acting "constructively" in an advisory capacity, which entails liability risks).

Real or virtual makes no difference; if the expert leaves their task of assessing, it is consulting and then they are fully liable, possibly also for the executing company. Even if there is no contract and no payment, even if it is a favor between friends. Several engineers/architects have already broken a sweat in court because of this.

Execution planning and site management are not for nothing the core part of planning. If this does not exist, the client is liable anyway and it is their decision. If the client wanted to save money beforehand, this also counts in court, because a general contractor or craftsman will be clever enough to provide working plans. Some state building codes even require execution planning. This is about protecting the investment of the client; a building authority has no further interest in this. Unfortunately, there still is the "little site manager."

The KfW does not save any client here either, because the required specialist planning is also regarded as working planning. An energy consultant is not liable here, as they do not prepare execution planning either.

The execution planning and construction supervision are not for nothing the core part of a plan.

There are also cases where in the end, the client still ends up bearing the costs.

Maybe it can be minimized, but I think if craftsmen know what they are doing, then site managers are superfluous.

My brother was once a master heating engineer, he never had a single case where a site manager told him: "you did that wrong"..... always clean work and did it out of passion, he had to change professions due to his age.

I am friends with a shell construction worker who has been doing it for 25 years, he has been working for 25 years with a very picky architect (also active as a site manager), who at the same time is always the client (then sells the properties). The shell builder lives for his construction sites, he is reachable until midnight and you can always ask him something without him becoming unfriendly.

Craftsmen should be checked more often, proofs etc. should be shown..... then there would be much fewer bad apples...

Maybe I also have the wrong perspective... no idea

The problem with the heating installer is that the manufacturers try to sell packages. I think almost every one of my clients has had to buy more over the past years than they needed. There often aren't even such small systems for KfW55 and better. Theoretically, from next year on, only passive houses will be approved for new construction, if the building energy law comes this year. And who are the craftsmen, which German still wants to be a craftsman? Usually, one is glad to be able to communicate with a craftsman. And the saying: "that's how we've always done it" is also not uncommon. It's not about working against each other. Every craftsman will prefer clear specifications. Often, the responsibility is shifted onto the craftsman, following the motto the last ones get the worst. And where is the problem in sitting down in advance with the craftsman to possibly coordinate planning according to his possibilities. For example, in timber construction. Compromises are something for existing buildings, not new construction. The craftsman also wants his full money for installing the windows.