The biggest factors for most goods is whether it is personal or commercial, class of goods, how you import it and what the dollar amount is.
As a flight passenger, you get $800 per month of tax-exempt goods for
personal
use. Many countries including Germany refund VAT at the airport if you purchase goods over a certain amount.
For shipping goods, it gets more convoluted but generally there is no import taxes for moderate orders (non-commercial):
http://www.cbp.gov/trade/basic-import-export/internet-purchases
Some shippers (UPS) send everything through a broker and you pay those fees even if it has no import taxes. (I got charged brokerage fees for importing original art from a college student though that class of goods is exempt.
In short retailers, pay more taxes than an individual who often does not even have them.