The apartment is nice and its location is great. No complaints in this regard.
We had 2 issues, though.
First was the check-in. The host's friend Benjamin was not able to come in person, so my friend had to deal with a lady, which doesn't know a word in English. This might be a problem for someone who doesn't speak German.
The other issue we had was the lack of cleaning service.
The bed sheet and the covers for the pillows weren't new. Also there were freshly washed clothes hanging on a dryer in the kitchen area. They stayed like that for the entire time, because the cleaning lady never showed up during our stay.
Charging €30 for a service without providing such is not okay.
Hopefully that is an isolated case and there are/were no other guests experiencing this.