What you need to look for on the tag is the Kanji 海賊版, which means "pirated." They can be pretty damn expensive, but if you see any toy in a Mandarake store with those Kanji on the sticker, then it's a counterfeit.
No offence, but if I saw those JP characters stuck on a box I wouldn't be able to tell them apart from any other JP characters at a glance.