I keep my sales records with the selling price of the item in the approriate currency and with the location on the buyer.
Going back to May, most of my Canadian dollar sales have been to Americans. None have had any problem with paying promptly.
I have had a slightly raised number of overseas sales from my CDN$ listings, but that has been going on for about a year.
Since I had to read your explanation of the Buy it Now offer a couple of times to understand it.
The BIN was $75CDN plus shipping.
The offer was $50US including shipping.*
You agreed and told him the invoice would show a price of $75 CDN, which is $56 US but would include shipping.
He refused your counteroffer.
I suspect that your buyer just lost interest during the haggling.
Ah well, anecdote is not data.
*Offers are not supposed to include shipping, btw. The idea I imagine is that most of the shipping fee goes to the carrier and is a fixed cost for the seller.