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How do I get a Tax Exemption Certificate for export from the US if I am in another country?
Assuming you are being charged sales tax, it all depends on where you take possession of the shipment. Are your suppliers shipping to a US address, say your freight forwarder, from where you handle the ongoing shipment, or directly to you in South America? If the latter, per Michael Pryor's answer, you should not be charged sales tax. If the former, if the address is in a state in which your supplier has a physical location they will have to charge sales tax. That said, your freight forwarder should be able to furnish your supplier with a letter stating that the goods have been exported (with a copy of the relevant Bill of Lading) which will allow your supplier to refund you the taxes (a company I was at before would allow refunds up to two years past the date of sale per various tax regulations). Alternatively, you could see if just a letter of intent from your freight forwarder is enough to not charge you in the first place, but that's technically not proof of exportation. You might be able to get a refund or an exception from the state's tax department directly, but I would recommend going through your supplier - much less hassle.