Duty-free shopping is governed by strict regulatory rules established by international customs authorities and airport security agencies. Key rules dictate that shoppers must be traveling on an international flight (often requiring presentation of a valid boarding pass and passport at checkout), and purchases are subject to specific country-specific import allowances upon arrival at their destination. Additionally, liquids, aerosols, and gels purchased in duty-free must comply with secure tamper-evident bag protocols if carried onto connecting flights.