Despite consumers declared interest, bookings of sustainable tourism products remain low. The key to bringing together supply and demand of tour-operator products is effective sustainability communication. Therefore, the aim of this study is to analyse the role of sustainability communication in the attitude–behaviour gap; little is known of theoretically and empirically. Semi-structured interviews were conducted in an ex-post investigation with customers of certified tour-operators. The participants neither perceive, recognise nor comprehend the sustainability characteristics of the products. To analyse the reasons, we use the value–belief–norm theory to depict how and why these customers process sustainability messages. The driving and impeding factors of successful sustainability communication are derived, and ways to improve the uptake of sustainability information are developed.