My first used figure from amiami arrived and I expected the worst possible box you can imagine if they rate it A/C... Long story short: I would sell that more or less as new lol Only the display windows is a little loose. For 1500yen I can't complain.
Japan's criteria for used stuff is vastly different from ours. I bought a shitton of used games over there and even some of the older ones (Famicom, Sega MkIII) were insanely well kept. The more recent stuff could pass as new for me (were it not for the plastic wrap). Same goes for the figures.
From what I see, most of the time amiami's "B boxes" or Mandarake's "箱小イタミ" pretty much equal "good as new"