Unfortunately, unless they have their email 
address listed in their profile, there is no way 
to e-mail the seller.  There is a spot where you 
can post a question and the seller (usually) will 
answer it.

Do you speak Japanese?  Does the seller speak 
english?   These are questions you have to take 
into consideration if you want to communicate (or 
bid for that matter) on YJ.  In my experience, 
most sellers do NOT speak english, and they don't 
always understand make-shift translations from 
machine translation. (ie:  elingo, etc.)  

Of course, if you know japanese and the seller 
and/or the seller knows english, you are all set.

jINx