I am in Canada but I think the US is about the same. So depending on where you buy from;
Customs and taxes are what the government charge you for importing an item.
- some sites pre-charge you customs and duties and pay it on your behalf (be careful that you get your money back incase you decide to return the item). I had a problem with Net-a-porter.com the international site. They wouldn't refund me my customs and it was such a hassle to get the money back.
- Other sites will just ship and the company or service will pay customs on your behalf and then you pay them directly, or they bill you!
In canada we pay upto 30% of the value of the item...it is usually less than that though. Its luck of the draw really.....