It doesn’t sound like he did.

Laundromats would have been ideal for this kind of, well, money laundering. In a pre-digital era, who’s going to check that the number of cycles on the washing machines line up exactly with the takings?

An auditor or private investigator, but granted, there's a lot of room for tax evasion - there's a reason a lot of businesses and contractors will gladly take cash, tax evasion being one, most digital transaction costing them money being another. It's fairly common in my country (NL) to see signs saying "please pay in cash" and "€0.25 surcharge if paying with debit card for amounts below €20"

Around where do you live? Anecdotally, I don't see much of any of that in Eindhoven or the surrounding villages.

Correlating with water and electricity bills could raise suspicion, but yeah, it's probably harder.

Maybe? Pre-digital machines would keep no tamper-proof record of usage. And a good variety of machines in your laundromat (with varying appetites for water and electricity) could discourage all but the most fanatical of auditors.

Hm, what about vending machines with things you make yourself, legitimately without any paper trail that would show what you are making?

And ideally the deliverable would be something digital rather than tangible so your COGS are effectively zero… like a bitcoin ATM for instance… hm

I wonder how he explained (or if he ever had to) that his weekly haul, deposited at the bank, apparently doubled when the looney coin was introduced ?

Having an actual fleet of vending machines would be an excellent cover for such a scam, but even if they're unprofitable, you still need do do some amount of work to maintain that cover. Soon, the cover story becomes an actual 'job' and you have to wonder if you're pulling in enough cash with the crime to rationalize it.

If anyone asks, tell them the receipt comes out if they shake it!