> Let me tell you I know why you don't see an "Amazon of Japan", apparently in here I'd have to calculate the sales taxes for every country where my products are sold through agreements of Japan-{said country}. Some countries don't even have agreements like Brazil so they are in a gray area.

AFAIK this is true for any other country, not just Japan. If you're in US, and you want to sell and ship products outside of US, you need to take care of the sales taxes and customs for each of the countries you ship.

Or you leave the burden to your customers, but they might not be happy to have to pay expensive custom to the mailman to get their package.