Regarding unfinished books, since Leanpub is a self-publishing platform, we don't typically have any knowledge of an author's life circumstances, or their writing project plans. Sometimes book projects can get stalled for a long period of time, and the author will come back to them.
So, the main provisions we have in place to mitigate any issue here, for people who are considering buying an unfinished book, are transparency, and our 60-day refund policy.
Authors with unfinished books show the percent complete and the date of the last update right under the book cover image on the book's landing page on Leanpub, so anyone who sees this before they purchase the book hopefully knows what they're getting. (Some people are actually happy to buy partially-written books that will never be completed, if the content it has is already sufficient to meet their needs.)
Here's an example of what this looks like:
If you buy a book and don't see any progress within eight weeks, you can just get a refund, and wait to see if the author publishes a new version with more content in the future, and buy it again. (We make it easy to get a refund within 60 days of any Leanpub purchase.)
Also, if someone buys an in-progress book thinking it was in fact 100% finished, they can also just get a refund right away.
Finally, we have a feature that lets people contact the author of a book they've bought, or that they're considering buying, to ask about the author's intentions for their book project going forward. We talk a little bit about that here:
We hope that helps!