Technically, an airline's system can result in double booking a seat, but it usually happens in one of two distinct ways. The first is "overbooking," where the airline intentionally sells more tickets than there are physical seats on the plane (expecting a percentage of "no-shows"). If everyone shows up, two or more people may hold a valid reservation for the same space, leading to "bumping." The second is a technical glitch where two different passengers are accidentally assigned the same seat number on their boarding passes. This is rare in 2026 due to real-time sync, but can occur during aircraft swaps or last-minute gate changes. If you find someone else in your seat with the same assignment, do not argue; simply alert a flight attendant. They will verify the manifests and, if the flight is truly overbooked, they will begin the process of seeking volunteers to take a later flight in exchange for compensation, which can often reach upwards of $1,000 or more in travel vouchers.