I normally visit shops such as Niniwa, Lucky Camera or Lemon who have a large selection of second hand vintage lenses rather than deal with personal second hand sales due to language issues. These all do tax free. I find that the shops are quite aligned in their grading system in Japan, and are very stringent on them, it could be that they value their grading as a form of business honesty to build loyalty with their customers. Having examined over a hundred of these lenses whenever I'm in Japan, I know off the top of my head what each grading is and if a lens is listed as a certain grade, I'll know the condition it is in. Personally, for a balance between price and quality of optics, I always go for the B grade.