In many countries negotiating or "haggling" on price is appropriate and expected.  Paying full price may be looked at as weakness or in experience.

Don't expect to have "satisfaction guaranteed" when buying an item.  That's a U.S. policy not found in most foreign countries.  Be sure that you are familiar with the return and exchange policies of the shop, vendor and/or country before buying..

Most other countries do not recognize copyright laws.  A logo may have nothing to do with the company it supposedly represents.  "Knockoffs" are common.  Look carefully to see if the item is a fake.

Be careful.  Many items need a special license for export.  This is particularly true with antiques, works of art and any items of cultural importance.

Often taxes are a bigger part of the total purchase price than the item itself !  

In some cases, duty free may indicate that the items are free from duty only where they are being sold.  Be aware that U.S. Customs may have their own guidelines for taxation when you return.

You can’t avoid paying it up front, but you can often have a portion of the tax refunded to you as you leave the country.  If the purchase is to be taken out of the country and not consumed in the country of purchase you are entitled to some refund.  You will pay the VAT tax on some items but be able to get a refund on those that you are bringing home as gifts or souvenirs.  Below are suggestions for getting some of your VAT tax back.

Check the tax regulations of each country that you are visiting.  Refund procedures and policies will differ by country.

Find out where you can obtain the refund forms.  It's possible that you may be able to request them from the country’s embassy before you leave.  If not, check with the local tourist office, customs office or at the airport.

Always carry your passport with you when you go shopping.  You will need to verify your foreign status to merchants.

Upon departure, arrive early at the airport and allow plenty of time for the VAT paperwork to be completed.

Never check luggage containing items that need to be inspected for a VAT refund.

Try to pack so that items that you need to have inspected are easily accessible to customs..

Be sure that you receive the proper inspection and stamp for all paperwork completed by the customs officer before departing the country.

Register with U.S. Customs before you leave, if you are taking foreign-made or expensive items with you on your trip,   If you don't, and can't prove that you already owned them, you will probably be charged tax when you return.  You can easily register with Customs by using the serial numbers of the items or showing them itemized receipts, detailed insurance policy information or jeweler’s appraisals.

Be aware of the amounts of arrival and departure taxes that you’ll expected to pay at Customs.

Don't try to hurry through.  Leave enough time for the normal Customs process.

Understand the restrictions pertaining to transporting foods, plants and animals across borders.

Record all your purchases and keep the original receipts of anything bought overseas.

Try to pack all items so that Customs can easily inspect everything.

Pay attention and follow all requests from Customs Officials.  They generally have extraordinary powers and can choose to enforce very rigid penalties if you are not cooperative.

https://help.cbp.gov/app/home   Read the U.S. Customs Service homepage.

http://www.cbp.gov  Check the U.S. Treasury Department Customs Service’s Traveler Information, Know Before You Go web page.  It contains information on U.S. Custom’s declarations, duty free exemptions, prohibited and restricted articles and the procedures for shipping items back to the U.S.

https://help.cbp.gov/app/home  Peruse the U.S. Customs Service Traveler Information web page. It contains links to the services the U.S. Customs Service provides to travelers.  In addition, some of the web sites are also individually linked to this web page for your convenience.