The new wave of self-publishing is both a blessing and a bane. I've self-published 3, and had 3 published by small press publishers. Still nowhere near the big time.
I started to write over twenty years ago and realized I didn't know good writing from bad. I was lucky enough to find and join a writers' group with two Eng. Lit Profs and a high school English teacher. Our goal was to hone our craft and become published. I didn't submit anything until I'd been with the group for several years and finally started getting published in magazines and anthologies. In other words, I paid my dues, because magazines won't accept writing with typos, grammar issues, etc.
As a writer, I make sure that EVERYTHING I write is self-edited at least twice, even forum posts. My writing is my reputation.
That being said, there's always a possibility of overlooked typos. But if you see a book blurb with poor editing, you can be sure there's a lot more errors between the covers.
Take care,
JohnB