No kidding, I would be so freaked out not writing tests the second money is involved. I just don't understand why he didn't bother to hire some help when things got bigger.
That's the part I don't understand – I'd be scared witless at the thought of not having tests for anything moving money out of my accounts. When you have millions in those accounts, even a really expensive developer is cheap insurance…
As soon as you write anything where a bug causes money to change hands, even on a laugh, you write some tests.