First off, in order to use Yahoo Japan, you must be 
able to speak/read/write in Japanese (not romagi!).
Second, the majority of the sellers will not trade 
with you because why should they if they can buy it 
in Japan for half of what you paid for it?  Even if 
they do, you will loose out on the deal due to cel 
values being lower in Japan.
My suggestion is for you to get a deputy service to 
help you out with these transactions.  The fee is 
normally 10% , plus expenses.
Good luck!

The Evil Jew