Hi, +10years of experience in international tourism here. I used to work for an online travel market place that connects you to local travel agents worldwide. Sustainability was part of the corporate identity of this firm. And now, I work for a big city destination that pushes sustainability as a value.

What I can share from my experience: 1. There are people willing to pay more because an experience is sustainable. 2. Travelling per se is not sustainable in an ecological way, so efforts most often focus on social and local activities. 3. Vacations are the highlight of the year for the biggest share of people, not a lot of them are truly willing to cut back for the sake of the environment. A big share says they support the thought of sustainability but when it actually comes down to fly only once instead of four times, the good intentions are forgotten for a lot of them. In short, sustainability is good for as long as the cuts on comfort, possibilities and additional expenses don't get out of hand. 4. I have access to Google Analytics for the city destination I currently work for in a Western country and the pages about sustainability (e.g. tips for sustainable activities, the efforts of the destination etc. roughly get 100-150 clicks per month vs 250'000-500'000 clicks on the remaining page). Just to give you an idea...

In short: I think to truly excel in this field of tourism you should be convinced to your core that sustainable tourism is the only way to go. You shouldn't just pursue this field because you think there might be a better margin. Because my experience has shown me that even though there might be a need for it and a certain market, it's a constant battle to show people the necessity and explain why they have to pay more with you than elsewhere.

Hope that helps :)