Does punctuation matter?
I am performing an inadvertent experiment to see how much difference it makes. I ran my book Cynthia the Invincible through Grammarly, and caught many of the infelicities that slip through word, libreoffice and the hemmingway app. It's not perfect, nor am I, but it seems to have improved the book's quality.
Smashwords gives two counts. One is the number of sample downloads and the other is the number of "purchases." The purchase/sample ratio is therefore a measure of the quality of the book.
My earlier books were averaging about 1/20. So far, although over a much shorter period the ratio is 1/6-1/7. We'll have to see what happens with longer times, but I'm optimistic.
Update. It's hanging around 1/7. So the details do matter.