The Japanese differentiate between goods sold in Japan and for overseas. Many people believe that cameras, etc. made for the home Japanese market are better than those shipped overseas. I tend to agree with them.
If the C6 from Ebay is a genuine made in Japan one and is sold for less than US$400, I would say go for it. They usually give you some kind of guarantee. Even though the made in Japan C6 only has a Japanese manual, there is no problem, because you can download the English one from this site. One can also change the language of the C6 to English and several other languages.