If it had been me I would probably have notified the first person who made the offer and given them the chance to get it at the full price. OTOH, if I knew the second person and liked them I probably would have just sold it to them without notifying # 1.

I've listed stuff with the buy it now CONUS and added that international shipping would be more. My most recent item was not a buy it now so that if it sold internationally there would be no misunderstandings.