Sometimes a problem. When I took a a cab from the Adlon to the main Station comment was: Only? Not great. In fact you donīt have many chances to enforce the drive. I would write down the registration number and complain about the driver. Most effective...

P.S. Once I wanted a cab from the main station to a relative far destination. 2 drivers ignored me as they seemed to thought I had Business to do in the inner city. In the end the taxi-driver who drove me was very happy as it was a one way 50 € drive, I allowed him to wait for me (no extra Charge of course) and my Meeting was only 15 minutes.