https://www.ustaxhelp.com/tax-help-us-amazon-sellers-living-abroad/ may help you to get started. You should review the specifics of the treaty the client is referring to. 

Why is it that every Amazon seller hates the US tax code?

There must be some irony in there somewhere.

Maybe start with Form 8833 and see where it leads you?  Good luck!

Thanks. I've reviewed the specifics of the treaty and I don't believe that an Amazon fulfillment center rises to the level of a permanent establishment of the NRA business. They have no control over what happens there and are simply paying for service. So I agree with the client.

Thanks. I reviewed the instructions for Form 8833 and see that report is specifically required when: "That a treaty modifies the amount of business profits of a taxpayer attributable to a permanent establishment or a fixed base in the United States"

The only thing I'm not sure on is Box 2 on the Form 8833 "List the Internal Revenue Code provision(s) overruled or modified by the treaty-based return position" Any idea what IRC provision relates to taxation of business profits?

Try googling  "26 us code chapter one". Go down the list, and select the one that applies to your client.

Thanks. Based on that it seems like the provision that is overridden by the treaty is 26 U.S. Code section 872 (a)(2). Seem right?

https://www.law.cornell.edu/uscode/text/26/872

(a)General ruleIn the case of a nonresident alien individual, except where the context clearly indic...

Just an observation:

- Has your client established a legal entity doing business in any country other than the US?

- Do the "permanent establishment" or "office or other fixed place of business" rules apply to individual taxpayers?

- Does your client's business have any other income sourced from the US or otherwise?

I"m not suggesting you have some form of "hybrid" structure.....but you might ask if you haven't.