Ladies and Gentleman,
I got feedback from Dachser who will forward our container. I just copy + paste it here. For me the case is closed

Dachser:
> The rates you received from our NYC office should apply
> without any further costs. However it can happen that
additional
> costs accrue if for example the following happens:
>
> - customs wants to see the freight/paperwork (customs
inspection)
> - the carrier does not accept the empty container at their
inland
> depot and we have to return the container back to the port.
> - demurrage/detention charges if we cannot return the container
> within the demurrage/detention free time we get from the
carrier.
>
> etc etc.
Me:
Can you please go into more detail regarding the risks you
mentioned? Like how can it be prevented, how much will it cost if
it happens etc?
Dachser:
> Unfortunately there is nothing what you/we can do against it.
> If customs wants to see your freight than there is nothing you
> can do and charges would be as per outlay.
> Same with the return of the empty container. If the depot is full
> and the carrier is telling us that they will not accept any
> further container than there is nothing we can do except finding
> another inland depot or we have to return the container to the
> port.
>
> Please note that this happens pretty rarely.