Some summary:

• Author got $20,000/- from publisher. $10,000 on sign up, and $10,000/- after delivering the final manuscript. After 10% cut of agent, author was left with $18,000/- for two years of writing and editing.
• They say it's good money (for independent press), their previous 3 books got them 4 digit advance (so, less than 10K).
• They sold 650 books to end up number 85 on USA bestsellers list.
• About 5000 books are also ordered by bookshops / sellers, so they are half out of 10,000 copies first print.
• Bookshops can return the books if not sold.
• Authors don't get any royalties until they have paid off the advance they get in the beginning. So in this case, until they have paid off the initial $20K, they won't get any money from the book.