Many Japanese sellers vastly over-rate what they are selling. I've seen items that were obviously badly scratched and rusted rated Mint-, not to mention that they are often very over priced. I find this distressing.
That is the case now. Until around a year ago, the opposite was true. I've bought a number of cameras and lenses from Japanese sellers, and my experience was always that they underrated the quality of the good they sold. I've bought Hasselblad, Nikon, Mamiya, Canon, etc., and they've been extremely high quality.
I've noticed, though that some of the items I've examined lately, have not been as high quality. I believe that part of that, is that the literal volume of used equipment, especially large and medium format is shrinking, and the "cream of the crop" is likely gone, except for the hoarded items.
In the mid-late 1980's, the Japanese were on buying sprees for collectible equipment, especially Leica and Hasselblad. They paid outrageous prices at the camera shows, and that equipment surfaced at what could be termed "bargain prices" in the late 1990's.