[freedomben]

I love buying pre-releas books from Prag Prog (which isn't exactly the same but similar to what you described). Especially since things change so fast, if you have to wait for a finalized, published version of the book, it's usually outdated by the time it even hits the shelves (not entirely of course, but parts of it). If the author(s) publish pre-releases frequently, it can be a fantastic reference.

[billme]

Preselling good, since sending cash is a lot better signal of interest than handing over email, SMS, etc.

That said, you would need to have a quantifiable definition of done and likely be a good idea to account for absolute failure in case something comes up an “done” is never accomplished. Until it is “done” likely be good idea to escrow the funds, but then you run into issue like paying taxes, transaction fees, etc.

[freedomben]

Agreed, escrowing is a great idea. In the case of the books I bought they were by very prominent people so I had high confidence they would be completed. For less-known authors tho, you make a great point.