We've been selling books using Amazon, Barnes & Noble, and Smashwords. The first two are easy: I make an epub file with Apple Pages and load it to the site. Smashwords, which I love for its can-do little-guy spirit, has almost always been a nightmare for me, because they wouldn't accept submissions as epubs. When I heard that changed, I cheered—
—and then discovered new nightmares. In the hope of saving someone else, this was the solution:
1. Unlike Amazon and B&N, Smashwords wants a cover image inside the epub file. The size specs are here.
2. Pages will let you put an image at the beginning of the file, but the epub that it generates will fail the Epub Validator, telling you there shouldn't be any div commands in line five of the cover.xhtml.
3. In order to edit an epub file in OS X, you can't do what you do in other systems (which is to change the file name from epub to zip, unzip it, edit it, zip it again, then change the file name back to epub), because the new epub file won't be formatted properly. I've only found two ways to do it, using the Terminal or using these Unzip and Zip EPUB files. I chose the latter.
4. I opened the cover.xhtml file in TextEdit, deleted the div bits, and packed the file up again. Smashwords seems to be happy with the results—if that changes, I'll update this post.
But the next time I make an epub file to sell, I'm going to try Sigil.