>850€/m2. How on earth is that supposed to work?
Was that a rhetorical question? With a flat rate fixed price, that doesn't matter; it only becomes interesting if one contractual partner does not or does not want to adhere to what is contractually agreed. But then it is not even worth the paper it is written on. HOWEVER, they of course know that too and try to solve it the way we do: they simply don't deliver what was contractually agreed. And then it ends in no delivery at all. Construction stop. Or you get builders (neighbors of ours) who moved in roughly on time but got ripped off and in the end paid for the interior doors twice: once to the general contractor and once again to the craftsman. And the general contractor calls that his personal profit. Note: we never had such an inexpensive contractual partner, but nevertheless some try their luck.