The mere absence of duty or other taxes on goods being sold does not assure that they are bargains. Costs of identical goods from different duty-free sources can vary widely. They often depend on the presence or absence of nearby competition, e.g., airport stores, especially if all at any airport are owned by a single firm such as Dufry. Also, prices can often be driven upward by the costs of buyer convenience, e.g., in-flight sales by airlines. Many airlines, such as Emirates, El Al, Middle East Airlines, Ukraine International Airlines, Delta, and Avianca,