I know this is off topic...

I wouldnt send items off to certain countries and just blocked these people from these countries.

Ive seen sellers state in their listings they wont send items to these countries, top three being,

Italy

Israel 

Russia

Some US sellers also block people from Australia from bidding on their items as well.

Regarding to the real topic at hand, don't worry about it, just add them to your block

list, sometimes buyers like to "push" sellers to see how far they can go. Your negative

feedback will go back to 100 % after a year full of good positive feedback, so maybe 

concentrate on getting double the amount of positive feedback. 

I've seen sellers from the USA and China have 30 negative feedbacks to their 2000

positive feedback and people are still buying from them. If you sell quality items,

people will still buy from you. But as a buyer, I wouldnt bid on items from sellers who 

have 96 % and lower feedback.

Hope that helps!