This kind of Internet business is fine. The problem arises when terms (including customs duty and taxes) are NOT CLEARLY specified on the suppliers web page and the supplier has made efforts to avoid taxes such as marking items as samples/gifts etc...
You are the one taking the chance with customs. If they don't check it, good for you, if they do, pay up. But you as the consumer need to be aware of this when you purchase the goods and you also need to be informed of the cost of the duty/tax incurred before you make the purchase. If you are not informed, the supplier is liable.