They were available on the phone, and when power went off, and security switch did not wanted to go back, they send somebody pretty fast to have a look.
When I lay down on the bed in the upstairs bedroom, it felt like I sank in by roughly 10-12cm, deep enough that lying flat felt impossible. I reported this 40 hours after our arrival, and I also said that because of this we would probably leave the house one night early and rent an apartment elsewhere instead.
This, of course, is the polite signal, where you give the provider a chance to fix their mistake and offer some kind of compensation. I assumed that after a message like this, they'd realize on their own that they should refund one night.
They didn't take that step.
After that, I wrote to them that because of the - in my opinion - unacceptable mattress upstairs, and the safety switch taped over with tape, and I was asking them to refund the one night we didn't even spend there.
They wrote back saying they'd check the mattress and let us know. Next day they said that according to them it's fine, some people like a soft mattress, and they're not in a position to credit one night.
I like a healthy mattress, one where the neck and spine don't have to lie in an abnormal position at night.
A disappointing experience. Correct-looking communication on paper, but no compensation.
We paid 868€ including the cleaning fee for 3 nights, 3 people.
That's 289€ per night. For that price, everyone expects a much better, more nicely furnished house.
Oh, and the house faces a relatively busy street. We do not recommend renting this house.
Update: The Business Manager of the company who rents out this flat, wrote me 21 days after i published this review. In his 1st e-mail he suggested my earlier correspondence could meet the legal definition of coercion or extortion under German law, and asked me to delete the review by a deadline or he'd pursue further legal steps.