For Europe custom, most of they are really bothersome.
They charge tax for a bag of cloth that I send to my girlfriend for daily use...
Although I claim only $50 USD
From company to customers:
From 0 to 22€ for small package you have a very low percentage that customs will open the package and charge you.
From 22€ to 150€ and for relatively large packages you have a high percentage that they will open it and charge VAT and handling, depending on country of destination, in Italy it's 22%.
Over 150€ they open and inspect the package and there's an additional tax which in English I think it's called duty and varies depending on the content of the package.
From person to person internationally:
From 0 to 45€ for small package there's a low percentage that they will open the package, and there's no tax.
Over 45€ is the same as from vendors to customers.
So either way you have to pay at least the VAT of the country of destination which in many European countries is above 20% value.