We know several people who have self published on Amazon and a couple actually have made a worthwhile amount of money. I have some videos up on YouTube about reloading and taking apart and cleaning various firearms. I have gotten 474,000 views and received several hundred dollars. None of them were serious projects that I did any serious planning or editing on. I have often wondered if I applied myself... if it couldn’t make significantly more.
Selling an electronic pdf for profit is no different than asking money for one’s emails.
By the way, I charge $8.79 to read this electronic post. Got PayPal?