Hello everyone,
first of all, it should be noted that, as far as I know, there is no legally secure basis or definition for the term "Schlüsselfertig" [turnkey]. A judge would certainly see the term "Bezugsfertig" [ready for occupancy] differently.
Therefore, it depends on what is stated in the contract and the service descriptions of the respective [Schlüsselfertig]-provider. For example, it may be the case that all connections (water, sewage, electricity, gas, telephone, etc. including all associated work) are not included in the offer price and that the sewage pipe only extends 1/2 meter out of the foundation. Here, I can only advise utmost caution; if necessary, a specialist lawyer for construction law should be consulted, because a layperson is certainly overwhelmed here. Especially in this field, there are many black sheep. Furthermore, the construction of a building by a [Schlüsselfertig] manufacturer can entail unforeseen and serious disadvantages, even dangers, which can become very, very expensive for the builder.
Here are just a few points briefly noted: Very important: never make advance payments, but only according to construction progress! But who monitors that? Who exactly (which craftsmen) actually performs the work on the new home and at what price? Who inspects this work? If trades are to be carried out as own work, do I get reimbursed the actual costs? Would I get another craftsman for the same price? What actually happens if the [Schlüsselfertig] builder files for insolvency during the construction period????
I hope I have not unsettled you too much with this and have nevertheless helped a little.
Best regards