Used watch shopping in Tokyo

Any suggestions from WC on shopping for second hand (er, used) watch vendors in Tokyo? I've made over 30 business trips to Japan, but not once have I shopped for watches. I'm familiar with Ueno, Shibuya, Ginza and other districts. Am looking for Grand Seiko Spring Drives and/or Rolex Explorer II/Milgauss/Air-King. So, do you have a store(s) to recommend? And what should I expect in terms of the transaction (credit card, any taxes, discounts for foreign passport holders?). 

Thanks - really appreciate this community of enthusiasts! 

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Reputable dealers with proven authentic product. Otherwise treat everything as fake and pay accordingly. Go without a watch and wear it back or pay customs fees.