Not all gurus operate the same, but if a person is a legit guru, they should have no problem managing to meet the demands of their biological vulnerabilities. Some aspect of their modus operandi would lend itself to such an income.

If they're someone like Eckhart Tolle or Sadhguru or Gopi Krishna, they might earn some money from selling books or speaking engagements. If they're someone like Bentov, Tesla, or Da Vinci, they might earn money by their genius inventions and ability to understand the universe in ways others do not. If they're someone like a Buddhist monk, they might simply be content with whatever is donated into their donation bowl each day.

I like applying an economic lens to such things. For example, Dr. Robert Gilbert's time is very valuable as the things he teaches are in high demand. He has a lot to teach but only so much time to allocate towards various endeavors. He understands the value of the material he teaches and of his own time, so, to scale his ability to educate people, he has paid online courses that people can choose to sign up for. I have no problem with someone earning an income by selling access to video lectures especially when he gives away a lot of information for free in interviews and on his own site.

I am prone to think that it is ideal for a legit guru to have passive income streams set up like books or courses because that frees the gurus time up to work on other books, other courses, etc. Ideally, eventually, proceeds from such income would be more than enough to handle the guru's own needs and the excesses can be put towards other pursuits like establishing centers for spiritual growth, charitable organizations, schools, etc.

Real gurus shouldn't need to resort to shenanigans to fund themselves. If they really have something legit to share with mankind, they should be able to get a following of supporters willing to voluntarily offer value in return for value received from the guru. This can manifest in many forms.