Is consulting a building expert shortly before acceptance reasonable?

For defects that are still found now, yes. Drawing conclusions about other trades from that... Why should the concrete worker have botched the job if the electrician installed the sockets crooked? Such "extrapolations" work if the entire service comes from one company, but only very limited if you judge 25 companies based on the performance of the last 4 whose work is still visible.

By the way, it doesn’t contribute to a peaceful sleep either when you convince yourself that the wrong reinforcement steel might have been used in the floor slab because the screed worker messed up 2 windows with splashes. You can't change it anymore anyway, even if there are 2 mats missing in the reinforced concrete.

What kind of massive defects are we talking about that can still be found during the preliminary acceptance and corrected within 2 months? It’s hardly going to be about the windows being installed incorrectly or the bitumen membrane missing under the first layer of bricks.

What do you want with a house where you yourself doubt the correct execution of the foundation according to the structural engineer and geologist?

There is this person called the site manager who is actually responsible for preventing botched work or reporting it immediately. If botched work remains at the final inspection, the site manager has not done his job, and then it can be assumed that botched work in the other trades was also not sanctioned.

There is this person called site manager who is actually responsible for preventing shoddy work or immediately reporting it.

However, this job description only applies to YOUR site manager (architect or accompanying expert). The "site manager" OF THE GENERAL CONTRACTOR has a completely different job description: 1. to let themselves be called by the same title in order to lull the client into the misconception that they have the same function; 2. to mediate between the subcontractors; 3. to respond to delivery delays or faulty deliveries and reschedule workers accordingly; 4. to rectify shoddy work without affecting profits or to hide it until the warranty period expires. As you can see, the overlap is zero; except for the title, the two functionaries have nothing in common.

If shoddy work remains at the time of acceptance, the site manager has not done their job and then it can be assumed that shoddy work in the other trades was also not sanctioned.

With the client-side site manager, shoddy work has long been flawlessly corrected by the time of acceptance. The "site manager" on the general contractor’s payroll, on the other hand, has failed to meet expectations exactly when the shoddy work becomes obvious to laymen. The caught subcontractor is supposed to fix shoddy work at their own expense and without disrupting operations; the caught in-house employee, in effect, in unpaid overtime and with materials deducted from their wages.

P.S.: That builders confuse the general contractor "site manager" with a customer satisfaction officer is intentional and unfortunately incurable.

600€ is not even worth considering - do it!
Definitely hire an independent expert.

Hello everyone,
thank you very much for your assessment. It helped me with my decision. I will report on how it turned out.

However, this job description only applies to YOUR site manager (architect or accompanying expert). The "site manager" OF THE GENERAL CONTRACTOR has a completely different job description: 1. to have the same title in order to lull the client into the false belief that he has the same function; 2. to mediate between the subcontractors; 3. to respond to delivery delays or incorrect deliveries and to reschedule workers accordingly; 4. to fix botched work without affecting profits or hide it until the warranty period expires. As you can see, the overlap is zero; apart from the title, the two role holders have nothing in common.

With the client-sided site manager, botched work is flawlessly fixed by the time of acceptance. The "site manager" on the payroll of the GC, on the other hand, fails to meet expectations exactly when the botched work becomes obvious to laypersons. The subcontractor caught is supposed to fix botched work at his own expense and without delaying traffic; the caught employee of the GC, roughly speaking, in unpaid overtime and with materials deducted from his wages.

You speak directly to my soul. This is exactly the kind of "site managers" we got to know. I have already reported the result: 3 months delay shortly before the planned move-in and a 4-page list of defects in SG 10 which is also incomplete. Good that we are sitting on a proper final payment.