Books you think will sell can disappoint you. It is very difficult to judge which books will sell and which will not sell. So before locking yourself into a financial investment, it is a wise decision to test the market. I suggest testing the waters by formatting your manuscript in e-book format and marketing it on Amazon.com or Barnes and Noble.com before committing to a printed book.
Sometimes the book's cover design or title can hold your sales back, while other times it can be the way you present your content. E-book can be edited and updated on marketing sites with no consequence to the author. So it is a great idea to evaluate your book's potential before investing in press cost..