Responsibility of the architect in case of KfW interest and further matters

I cannot place this statement. The awarding of the shell and civil engineering work was obviously the result of a tender using the bill of quantities and awarding process. That means the most economical offer received the contract. The prices were known beforehand, simply and straightforwardly the quantities were poorly estimated.

However, we only received that one offer. And only the overall contract without the completed bill of quantities. We only got that last week upon request.

I do not want to claim that I recognized any usury. And of course, in hindsight we should have demanded the bill of quantities. But since the architect thought it would fit the cost planning, we trusted that.

What do you mean by saying that we are making it difficult for ourselves?

You are making it difficult for yourselves by making (procurement) decisions with limited expertise and incomplete, partially inadequate basics under unclear conditions.

But since no other offer from another drywall contractor was submitted at all, I almost suspect something like that by now.

Where did that come from all of a sudden? And what does that have to do with shell construction and earthworks?

Sorry, structural engineer. I'm already feeling all flustered.

Yes, for the following trades we will go through every single item and only when everything is clear and any follow-up costs have been explained will we sign.

I take it all back: We naively thought that the architect would act on our behalf and not that he would passively cause us financial harm. Now that it’s becoming clearer, we also realize what a risk this item was.

Not to bother you any longer: There really isn’t anything that can be done here anymore?

And for the future: Check and research every single item? That’s not exactly going to get easier with the upcoming trades...

Does anyone perhaps know of overviews for such exams?

go through every single item

Unfortunately, that only brings nothing if the service description/the bill of quantities is rubbish, and the quantities behind it are incorrect/random.
For example, in excavation and disposal, I am missing the installation class/assignment value (Z0-Z2). Just depositing Z2 alone costs >50€/t. Plus landfill acceptance fees, handling, and sampling, that already adds up to a nice sum per ton. The risk of having to dispose of Z2 material at your own expense is borne by hardly anyone/nobody when the specifications are unclear.

tl;dr: Construction costs in individual contracts stand or fall with the quality of the tender documents. If the bill of quantities is poor/unclear, high costs arise in individual items, additional costs due to increased quantities, and claims for supplementary payments, which are already prepared in the drawer before the order confirmation.