My own humbling experience at selling a book is this: MARKETING MARKETING MARKETING. Everyone who has read it has liked it, usually 5 stars. Doesn't mean squat.

If nobody knows about it, nobody is going to give it any stars. From what I've read, some people throw a lot of money at marketing their book, spend all of their time marketing etc. Some have hired companies to buy thousands of e-copies, so it can rise to top of amazon. The thinking there is REAL people will then buy it because it is doing so well. I don't have the time or cash to do that, (and it feels like cheating) but I also have a job, so it's a free time thing at best.

Friend of mine published through a publishing company, through an agent etc. (just finding an agent can take years) It was an amazing experience, but in the end, the advance was spent on the publishers recommended marketing agent, who was terrible.

Best advice I can give is write what you love and put it out there. Don't give up on your dream, but don't give up your day job either. Good luck!