... Or simply delete a check or entry and invalid financial statements. Fraud controls like vendor level tracking and requiring a reversing entry to adjust balances are hard to find in Amiga circa 80-90's software 
.
This is true, none of the software from that era can do proper anti-fraud measures, they are NOT implemented. At all.
I guess it would be possible on some solutions to add those controls via an Arexx port, if that software has such a port that gives forwarding and receiving commands to the accounting system. It is no trivial thing to do that do any good measure. Don't do accountancy for somebody else, but a company does itself not have to comply if they are doing their own accounts. They still have to keep fair accounts and present them for auditing. In England and Wales, they do. "fair" covers quite a bit of ground here.
You could not do that live on an Amiga, hooked up to the internet, doing other peoples accounts, using an Amiga. You could do it on an Amiga, entering data manually. That's two different things entirely. Hooking it up to a network is a little risky. Keeping it offline and feeding written or printed data to it (easily kept for verification) is the more sensible way to go. You don't need accounts to get second by second updates of stock expenditure usually. If you have lots of data you could burn that on a CD-ROM and feed it. You also need to securely record the information you get back out of the accounts package. For further verification, obviously.
I did a search of aminet on "Finance", nothing usable in itself for purpose, some demo contenders maybe, also good demo if you want to learn how Stock Exchanges are played, for real money, in the real world (it's a sim, don't get that amazed).
http://aminet.net/search?query=finance
