Tourist destinations are increasingly coming across multiple social, economic, cultural, and environmental challenges corroborated with a great urgency for sustainable development. In this context, the European Commission has launched in 2013 a unitary system of indicators for sustainable management of tourism destinations, called The European Tourism Indicators System (ETIS). More specifically, ETIS was configured initially with a total of 27 core indicators and 40 additional (optional) indicators. The purpose of this paper is to present the difficulties and challenges encountered in the application of ETIS, having as a case study, the county of Braşov, located almost entirely in the Romanian Carpathians. In this regard, a testing technique has been designed through an innovative Group Decision Support System (GDSS) that is applied to our destination. The results show that the selection of ETIS indicators is a flexible process that must be adequate with the particularities of each destination taking into account both the needs of the stakeholders, the information that is useful to them, and the existence and periodicity of the data available. Also, in some cases, when the available indicators are insufficient, additional indicators have to be introduced, and they must be subsequently adapted to the needs and specifics of the destination.