It's not criminal per se. It's all in the law - they just aren't perks available to the typical employee. The cash jobs are but they're in a business where they can get this; a typical engineer can't ask to be paid in cash from a large corporate client even if they are freelance. In Australia it isn't that hard - people often can't get tradies here and as a tradie you are spoilt with calls for work. I personally know some pretty rude tradies that constantly get work anyway despite doing bad work. Getting a tradie to travel more than 5km to do work around my house depending on the trade is hard; they have enough work within a 5 K radius not to bother. They can charge what they like and typically do. Especially for the top end of town.