What are some serious side-hustles that no one talks about?

For example, driving lessons cost at least $50 an hour (lowballing), and on average people *probably* spend $500 per person. So 10 customers = $5000.

The cost to become an instructor is between $4000 - $10,000 (you need to take and pass an approved driving instructor training course). If you get good at generating good word of mouth, it could be a great side hustle that could eventually pay off long-term. (any driving instructor here who could verify?)

Of course I know its not as simple as this - nothing is.

But I just started thinking about different types of sidehustles and wanted to know what else was out there.