Buyers responsibility to check for any potential taxes or import duties. The seller can't be expected to be aware of these for every country they ship to, they are charged at the point of import and the seller has no control of them.
Caveat emptor.
Absolutely right. As a seller I have 90%+ foreign sales, and about 35% go to the US. In 99.9%+ of sales I have no problems, if I may say the buyer has hopefully learned something, although import duties and taxes in the US aren't generally as punitive as they are in the EU for example.
However, if I may put this into perspective, Brazil has to be the worst. I had one instance where a $200 sale ended up with the buyer refusing to pay duty, which was in the region of 100%. The carrier then (a) charged me the Brazilian duty, (b) charged me for the privilege of sending the item back to me and (c) icing on the cake was that I had UK duties taxed on the my own returned shipment. I had asked the carrier to destroy the item in Brazil bearing in mind the 100% tax, but apparently I still had to pay the Brazillian duties anyway. That $200 sale cost me $300.
As an aside, people, please don't ask or expect foreign sellers to falsify the value of items for customs purposes. It may be common practice on China exports but elsewhere in the world not all of us want to attract the unwelcome interest of tax authorities, and falsifying customs value is a sure fire way to do that. After all, in the view of the tax man, if you fiddle that, what else are you fiddling?