Nigerians can use proxies too. They use hacked accounts, they use anything they can. The only way to stop them is to get payment and let it resolve so they don't charge it back. This alone could kill your business, I doubt there is a very good way to stop this or else we would all be able to use it and stop from being scammed.
Blocking Nigeria would not help at all, they have access to other countries and they use proxies as well. Just know the basic scams and re-list, there might be a better way.