To do so fraudulently seems like a really good way to go to jail, though, no? And, as a requirement to hold your business account, the authorities know where to find you to put you there should the need arise?

Of course. But that's what were discussing here right, ways people might commit fraud. If people can popup businesses for fake, fraudulent jobs, I wouldn't think this kind of fraud is out for them either. And in some jurisdictions, being hard to trace as a business beneficiary is actually not difficult.

It surprised me when I ran a small business my bank didn't even require me to file the signatures up front. I just typed in peoples IBAN, the amount, and got it. They never asked for paperwork ever. Naturally, I didn't commit a crime, but I'm surprised with the trust.

So, yes, keep your IBAN secret, it can be enough for someone with criminal intent.