Many airports now have an excellent selection of local and high-end shops. Duty free deals, which avoid some import duties and taxes, can be a great bargain…but it’s not always the case. Savvy shoppers know how the airport or duty free prices compare to the retail price at home.
Here are some comparisons:
http://www.travelandleisure.com/articles/duty-free-deals
More good advice:
https://www.skyscanner.com/tips-and-inspiration/when-to-shop-at-duty-free-stores-and-what-to-buy
https://www.tripsavvy.com/duty-free-a-good-deal-459050
Lead. Travel. Pray. 