Man, I didn't know this would get so many responses, and I wished I could remember better from 30 years ago. So I apologize for the lack of detail (and I'm not a tax accountant anyway, so do not be taking this as advice or anything but an anecdote). But as I fuzzily recall, just put it in the "other income" box, deduct cost of goods, sorted.

One should also note that (as far as I can tell) the IRS does little more than a cursory glance at most returns to make sure the numbers add up, especially back then. Point being is that it's entirely possible one could have put "income from trafficking under-aged children into white slavery", deducted the cost of acquiring said children, and never gotten flagged because the numbers add up and it doesn't hit the "trying to weasel out of paying what's owed" flag in the computer. Dunno, I'm just relaying an anecdote with a lot of details left out, you sure as hell don't want to take this as tax advice.