Most everyone has seen a duty-free shop at the airport, and probably assumes that these are fabulous stores in which we are not required to pay tax on any of our purchases, however this term can be quite misleading. First of all, it is important to note that these stores are intended only for people leaving the country, good purchased at a duty-free store should not be consumed or used in the country it was purchased.
Also the merchandise purchased there is only tax and duty free for the particular country that the store is in. In other words, if you purchase perfume at a duty-free store at the airport in Paris, you will not pay French tax, but you will need to declare those purchases on your declaration form, and they will be subject to the same U.S. Customs rules and exemptions as merchandise purchased while you were traveling.
*Restrictions do apply in some cases, such as on alcohol and tobacco purchases.