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Here is the snap Koffing story: Experiences with Buy it Now on Mercari - #9 by Mussundwerdich
The difficulty here is that when buying from overseas, we have to rely on middleman services. It is very difficult to get a refund from these services.
Many of the Mercari scammers know that and they target overseas buyers like this
So most of us do not have the experience of buying from within Japan. I believe the buyer protections with Mercari are much stronger if you do