Ruined our wedding.
We had booked two apartments to stay in for our wedding, which Constantin had confirmed a few months prior to our booking. On the morning of our wedding he told me that only one was available due to Airbnb's system causing a booking error. From our side, there was no error from Airbnb - we had two booking confirmations, two receipts following the payments been taken etc. I think it was Constantin who made a mistake and didn't own up to it, or apologise. His lack of communication following this was poor, which caused a lot of stress. We had to pay to stay somewhere else and the groomsmen ended up sleeping on the floor the night before the wedding.
This flat had a blocked sink, the radiator in the bathroom wasn't working and was held on with tape. There was a beeping noise coming from the kitchen. One bedroom did not have a lamp. I would not describe it as a 5 star property.
I would not recommend staying in one of his properties.