This is true. There was an article in Exberliner a few years ago explaining how rampant it was for cafe owners in Neukölln to keep everything cash only and pay

This is true. There was an article in Exberliner a few years ago explaining how rampant it was for cafe owners in Neukölln to keep everything cash only and pay employees off the books. With such a high amount of foreigners and expats in dubious visa situations there's a lot of opportunities to play the system.