How can I know if the Post Office or Customs may charge some kind of tax?

I've ordered some supplements from the States and they say local authorities (like Customs) may charge some taxes... How can I get some information: I don't want to be charged extra.

Buying goods on the Internet is an increasingly popular way of shopping.

We hope the following will provide you with basic information about various charges, such as Customs duty, that may apply to goods you buy. You can also have a look at our Frequently Asked Questions (FAQs).

http://customs.hmrc.gov.uk/channelsPorta…

Its a case of lucky or unlucky!1 I bought an item worth nearly 3K from the US and dodged charges (sheer fluke) friend bought another item 200 pounds mobile phone and got clobbered for soemthing like 36 pouonds!

If it's over 18 pounds, they will make you pay VAT ans other stuff, if not... it's OK...