It's best to keep all the receipts from your purchases, so that you can challenge any official who tries to over-tax the items that you purchased. If you feel a duty is incorrect you can appeal the assessment or the way your clearance was handled get the badge number of the official and ask to speak to the supervisor. You may need to also need to write to the port director at your point of entry to clear up the matter.
Also, note that in the majority of Italian cities there are information points where you can go to claim back sales taxes on purchases you have made while in Italy. Sales Tax in Italy is 20%, which can start adding up to quite a savings if you have purchased many goods. So remember to save those receipts!
For all Passengers arriving in Italy from outside the European Community
For Goods purchased outside the European Community, or purchased in Duty Free shops the following allowances apply for travellers arriving in Italy from outside the European Community: 200 cigarettes or 50 cigars, 2 litres of table wine or 1 litre of alcohol.
When travelling between countries in the European Community you won't have to pass through customs. But, if you are planning to carry large quantity of goods you should check the up-to-date European Community regulations.
Travelling from Italy to the U.S.
US citizens may bring back up to $400 US worth of foreign goods duty-free if they have been outside the country for at least 48-hours (and if they haven't used the $400 US allowance in the previous 30 days). US residents over the age of 21 years can bring back 1-litre of alcohol duty-free. In addition, regardless of your age your age you can bring back 200 cigarettes or a 100 non-Cuban cigars duty free. Antiques, classified as more than a 100 years old by US customs can be brought back duty-free. The same rule applies for Original works of art made by hand.
You can also send packages of up to a value of $200 US to your home address with a maximum of one a day allowed. You need to label the package "Personal Use", it's not allowed to send perfume, cigarettes or Cigars via this method. Mailed items do not affect your duty-free allowance.
Tip - If you have purchased expensive items (Jewellery & Clothing) throwaway the packaging they came in, and when possible try to wear them. Usually the custom officials are more interested in your luggage than what you are carrying. Always remember the line " I bought this last time I was in Italy". Counterfeit products purchased in Italy like the Gucci bags you'll find available for sale by street vendors may look like a good bargain at 15€ or less. But, if the custom officials catch you with one of these items the fines will amount to more than you would have paid for the legitimate item in a Gucci store.
Travelling from Italy to the U.K. or other European Countries
If your journey was wholly within the European Community you won't have to pass through customs upon your return to your country. But, if you are planning to carry large quantity of goods you should check the up-to-date European Community regulations.