How does duty free actually work?
Duty free means goods sold without certain taxes that would normally apply — specifically excise duty and sometimes VAT or sales tax. It does not mean cheap, and the two are frequently confused.
The taxes involved are ones governments levy on goods consumed within their territory. Because duty-free goods are notionally leaving the country, those taxes are waived. This is why duty free concentrates on heavily taxed categories: alcohol, tobacco, and perfume.
Whether it saves money depends on the product and the country. On spirits and tobacco in a high-tax country, savings can be substantial, because duty is a large share of the normal price. On electronics, sunglasses and cosmetics the duty component is small, airport rents are high, and prices frequently exceed what you would pay online at home.
Several practical constraints matter.
Allowances are set by the country you arrive in, not where you bought. Exceeding them means declaring and paying duty on arrival, and the limits are often lower than the quantities on sale.
Liquids bought airside are usually sealed in a tamper-evident bag with the receipt. If you have a connecting flight, especially through a different security regime, that bag may still be confiscated at the transfer point unless the airport participates in a recognised scheme. This catches out a lot of travellers.
Arrivals duty free exists in some countries but not others.
Within the EU, duty free was abolished on internal journeys in 1999, so goods sold on those routes are duty-paid despite the shop's appearance.
Compare a couple of prices against home before assuming a saving.