I worked with a guy around eight years ago, who had a close relative who was your basic neighborhood drug/dope dealer. We got into this discussion one day. The relative was in her mid-20s, barely finished high school, and simply walked into some situation where she could flip drugs. He figured that on sales, after paying off the cost involved....there was $3,000 a week of income ($12k a month).
So I asked the obvious question....how did she really come to hide the income? Well....it was all cash. Her rent was paid in cash. Her food and beverages in cash. Her used car, in cash. She'd walk in two or three times a year to some bank deposit box and just toss in the range of $15k.
We went on with this discussion and eventually reached this impact point. There are thousands of people like her, and all are part of some underground business empire, with cash in a funny position. You really need to laundry the money and make it legit, but you don't want to draw attention. So you stick with the tested method of just hiding cash.
I asked....how would you event retire from the 'profession'. His take was that she'd eventually tire out, and maybe just quit one day in her forties, and walk away, if she wasn't arrested and sent off to state prison.
But you'd be sitting there with hundreds of thousands in bundles, and trying to put together a legit life, when the system just wasn't built to handle that.
This is one of the dozen odd problems with our society, in that we've created a mass landscape with financial affairs that don't fit the mold of our system today.