Getting happy customers recommend you to their friends and family to grow a loyal base is certainly applicable to the US. But the COL in developed nations is too high and the customer flow too limited to make dive instruction a practical full-time occupation.
In tropical vacation destinations, things are different. Most customers are on your island for the first and the last time in their life. Diving is another vacation activity to them, as important as kayaking. Customers sign up with a shop for a course, the shop gets them an instructor. It still takes good interpersonal skills to keep getting the gigs, but it's very rare that students would be looking for a specific instructor. Even if they recommend you to their friends, their friends won't change their vacation plans just to be taught by you.
Financially, it's not as bad as in the West; the money actually beats a min-wage job. But it's still very different from one. Works more like driving a taxi - take a short course, pick an agency of your choice (Uber, Gett, GASP...), pay it a tithe and serve your customers. Doing a great job will make them happy and better divers, but most of the time no one but you and them will know.
There's not much of a career to be made; shop management is separate from instruction, and the industry needs far fewer instructor-trainers, maybe one per hundred instructors at most. Some still rise to the top, but while in a typical corp about 30% will have some career growth and probably 5% will achieve social mobility, in diving the numbers are an order of magnitude less. Initial resources and circumstance can also be a roadblock; developing as a tec diver or opening your own shop is difficult on a rec instructor's pay.
More than the earnings, what limits one's lifestyle as a tropical dive instructor is forced mobility. Instructors normally aren't employees, they come on temporary visas, sometimes work illegally as work permits can be hard to get, and the high season doesn't always last year round. So the instructors go to where the customers are, and manage that with their visa stay limits. Nor are there any employee perks like medical or any kind of retirement plan.
Travel, visas, permits, fees, insurance, unforeseen expenses all eat into the income. Not that you can make much use of it - hard to own a lot of things when you have to pack your life into airlines' 20-40 kg luggage and carry-on, which includes your work gear.
It's a lifestyle for people who love to dive and love to teach, to the extent that this is all they need from life. Well, it's not that bad, you can have relationships and post on Scubaboard too, of course!