I travel a lot, and outside of the United States, countries have import taxes, especially on luxury goods. In some countries and iPhone Xs will cost $800 more than in the USA.

I have to visit the USA about 8 times per year, so every time I do I buy 10 phones in a state with no sales tax (usually Oregon) and make about $5k in profit selling locally (which does eat up a ton of time, but not $5k worth).