Additional costs - What does it include?

Rental agreements, like most contracts, do not have to be made in writing. So that is not a problem.

Small repairs, heating maintenance

Rental agreements, like most contracts, do not have to be made in writing. So that is not a problem.

Yep, concluding the rental agreement is one thing (and is already established by the permanent residence in exchange for regular payment). The absence of a verifiable agreement on the allocation of operating costs or the clauses on minor repairs results in these being borne solely by the landlord. But be that as it may, this aspect should not be widely debated. I would urgently want to change this situation.

Rental agreements, like most contracts, do not have to be made in writing.
So that's not a problem.

I have no problem at all with a tenancy without a contract.
But if something is not regulated in writing, as a landlord you have to live with the fact that allocations cannot be made. Quite simple!
Conversely, it is similar in that tenants, for example, do not have to take care of minor repairs themselves.

A contract by handshake simply has no contractual terms on which you can rely for claims.
Yes, it is not debatable [emoji2]

Thanks for the few hints, so it seems there is nothing now that I haven’t considered. Everything else that was listed does not apply to us.

Regarding the people who want to keep discussing whether there is a written rental agreement or not.
There is a very close family relationship with the tenant, so we have waived a written rental agreement. Yes, I know, that can be risky, but I am able to assess the risk myself and have decided accordingly.
So, now you can continue discussing if you want ;)

Regards
Specki

then it would be consistent to completely save yourself the hassle and simply agree on a flat rent