I guess the seller didn't really mean not selling 
to someone due to their nationality. I'm pretty 
sure that they wouldn't want to see their cels 
leave Japan. It happens most of the time with 
japanese sellers. 

But as mentioned, it is true that more and more 
japanese cel sellers are opening themselves up to 
sell internationally. But more or less, these 
sellers also make some reservations as to selling 
off very rare and nice cels to people living in 
Japan only.

That's why, they simply refused to ship 
internationally. Plus the fact that they have to 
deal with a language foreign to them (english), 
plus payment methods/shipping costs that 
sometimes buyers will negotiate to close the 
deal. It is a true hassle with the existence of a 
language barrier.