ebooks are put out by the publishers. I choose a book based on a story that I want to read. I don't worry too much about typo and other small errors. Some of the self-published stuff through Amazon gets fixed and you can upgrade to the fixed copy.
I had one favorite book that truly annoyed me because of the number of typos. Since I knew I would read it again, I wanted it fixed. I went into Calibre and copy and pasted it into Open Office. I fixed all the errors, saved it as a .pdf file. Then converted it to epub in Calibre. You can do this with any book that opens in Calibre and it's not actually a lot of work, but sort of pointless if you are not going to read it again since most errors will not be found using spellcheck.