We booked at the Diament Plaza because it was a new hotel with a good location, close to the train station and walking distance from the conference center. When we arrived to check in in the evening, we were told that our room had been "destroyed" by the previous customers, and they had no other room available. They first wanted to move us to one of their other hotels which was 6km from the city center! We had to check online ourself to discover that they had another hotel next to the convention center. They did no propose it directly. We had to force them to check whether there was a room available. There was one, which we luckily got. But the hotel was much older and less comfortable (two uncomfortable single beds instead of a queen, from the 70s). They never offered us any refund or anything to compensate for the difference. We also saw other customers being told their room had been given to someone else, because they "didn't confirm their late arrival". Very bad...