I have bought several items from Yahoo Japan. You need to have a Japanese address to get a YJ account to bid. So generally you have to work through a third party service. It is worth while for expensive items that you get a good deal on because of the transaction fees and shipping within Japan. A lot of what you buy off Ebay or what you get from Bachido is shipped from Japan anyway so that cost is the same.
Generally I find the pictures and descriptions on YJ far better than Ebay and most sellers know what they are talking about. However this requires that you can read the Japanese (the translation programs are not very helpful) and really understand the different styles, equipment and materials. The quality of what is available off YJ is far better. The reality is all that stuff listed as “junk” in YJ is generally what is sold on Ebay.
I got a kouki Tsugaru shamisen with good skins that only needed a little work for ~$800 delivered to my door in California. I have never seen a deal like this on Ebay or Bachido. There is definitely some risk involved in buying any used item off YJ or Ebay, so I don’t recommend it for everyone. You know you can trust what you get from Bachido.
Steve, are you looking for a shamisen? I have chuuzao shamisen that I would like to sell. Being that I am in San Diego it wouldn’t be much to get it to SF.