Sounds like a great headline, but the details leave a lot to be desired. As a matter of fact, the German concept of a “flat tax” is an additional daily levy imposed on prostitutes, not a simple and fair system for all taxpayers. As a news report explains, German politicians are motivated by a desire to capture more revenue:

Germany’s Finance Minister Peer Stein [Ed. note: error in original report. the name should be “Peer Steinbrück”] wants prostitutes to pay a flat tax of 25 euros a day, according to a report in Tuesday’s edition of the daily newspaper Bild. Sex workers would still file an annual tax declaration and, according to the number of clients, the tax authorities would either reimburse them part of the daily tax – or oblige them to pay more, said the paper. … Prostitution has been legal in Germany since the beginning of 2002, and prostitutes in theory have social security cover, but like taxation, the system does not work well in practice. According to a 2003 report, the German taxman misses out on about 2 billion euros from prostitution.