Understanding US tax obligations for Canadian retailers selling in the USA?

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Hi there,

We are a Canadian retailer about to begin selling in the USA but before we do, I need to make sure I have everything down pat with the taxes.
As our distribution office is in Canada, so from my understanding, we will not need to collect taxes unless were shipping from a US location, and all we would need to do is inform our customers under 'Shipping & Returns' that they're liable for any import taxes, duties and customs fees, is this correct? Or will I need to be charging tax per state?