First of all, make sure that your old books are in good condition and are readable. Because, torn and burned books will not grab the interest of any one and these books will be of no value.
Assemble the pages properly if you think that they are dislocated or have become loose. It will help in increasing the worth of the book.
Now you have to research on your old books and try to learn if there is any new version came in the market or not. Also try to know that the authors of those books compiled any other work after writing these books. It will help you a lot in determining the value of your books.
If the authors of your old books could not produce more work later on then the chances are high that you will get more value of your books.
A difficult and important task is determining the demand of those old books that you have in your possession. You have to meet different experienced people and also visit different libraries for checking the demand of those books.
You should also consult to different literary people and also the librarians of local libraries who will give you a better idea about the value of your old books.
Usually old books with good condition become a top priority for many readers. The older the book is, the better its price will be.
You can also find the value of your old books by consulting the valuable printed sources like American Book Prices Current and Bookman’s Price Index. These printed resources are helpful in determining the price of old books.
You can also consult the online resources like Bibliofind which is considered a reliable source for determining the value of your old books.
If you have a huge collection of old books then hire the services of an experienced appraiser who will help you in determining the prices of all old books.