Some possible criteria:

Satisfied enthusiastic visitors bring new knowledge back home and encourage friends to share their experiences, providing continuing business for the destination.

The need to respect certain traditions and customs is understood in order that these survive so that local people are not offended.

Communities measure tourism success not by sheer numbers of visitors but by length of stay, money spent and quality of experience.

Tourists not only learn about the destination. They learn how to help retain its character while deepening their own travel experiences.

Development and tourist numbers are kept within acceptable resource limits and are managed so as to minimise any detrimental effects on the environment.
The needs of the host population are met by maximising participation and involvement in decision-making. Tourism businesses do their best to employ and train local people, buy local supplies and use local services.
Biodiversity is maintained or enhanced and allowing inheritance of natural capital for future generations.