There are lots of ways to make income that is not accessible to government recording, reporting, or taxation.
When you're rich, those ways are called "clever".
When you're middle-class, a vanishing species, those ways are called "fraud".
When you're poor, those ways are called "criminal".
Of the three tiers, the rich steal the most, at the least risk and the least punishment. The poor steal the least, at the greatest risk and the greatest punishment.
@GeePawHill
IMO, the complexity of the tax code, at least in the US, works to the advantage of the rich
so I am in favor of greatly simplifying the tax code
eg, the Wall Str Journal just reported that there is something called "private placement insurance" that allow weathly people to delay and defer taxes on weatlh