If you are the author of the book, as well as the performer (reader), then you can sell CDs. If it is somebody else's book, you will need permission from the author or copyright owner before you go forward.
It would be a good idea to have a lawyer look over any license agreement the copyright owner offers you. You may also want to have a lawyer negotiate with the rights owner to begin with.
To add to the other post, generally speaking the "audio book" rights of an author or publisher are zealously guarded. So if you are not the author, I strongly advise you not to sell these audio book readings online or in any other highly visible forum. It could be the gateway to a cease and desist letter and other nagging legal issues, if the books are of large enough stature. That being said, if these are very niche/small/independently published books, it might be a worthwhile enterprise to seek a license from the rights holders to sell your version.
I hope this helps.
Disclaimer: This answer is for informational purposes only and does not constitute general or specific legal advice, nor create an attorney client relationship.