If the front cover succeeds, your would-be customer will turn it over and read the back cover, giving it maybe 20-30 seconds to convince him to open the book and see what's inside. If you want to get the best books cover service then you can look for: firmware creative – Innovative Book Design.
For a nonfiction book, only then will the customer take time to look at the table of contents and, if that interests them, flip through the book for photos, eye-catching headlines, and sub-heads, and general layout, maybe pausing to read a paragraph here or there. Some people will take time to read the first paragraph or page, while others prefer to read the last page or paragraph (different strokes for different folks, you know).
Your book cover is, therefore, another key element in your book's success and one that should never be done on the cheap.
A good artist may or may not be a good cover designer. There's a lot more to creating a good, effective book cover than just good artwork. And be careful if you, or your designer, use stock photos or artwork, as the photo or art you choose might be found on other book covers as well. Do you really want to find your cover art on somebody else's book?
With virtually every book published on display on websites somewhere (Amazon.com, for one…but not the only one), you or your designer really need to consider how it will look when shrunk down to thumbnail size. Does it still have an adequate impact? Will it still cause a potential customer to pause long enough to find out more?
Designing effective book covers is an art onto itself. Learn as much as you can about it, even if you hire a designer, and browse the bookstore and library shelves to see what others have done.