I am a man so I have never worked as prostitute but Maxim has few girls who have been working there for years. This proves me that the club is fair and pay good money to girls. It is also located in Vienna downtown, most likely it is the safest part of city.
I agree, Innere Stadt is a very clean and safe district. Maxim is in Kärntnerstrasse what is one of the best shopping streets in Vienna. It is always full with people, there is a metro station, bistros, restaurants, so it is a very good place.