The value of an old book is determined by many factors, including the edition, the age, the rarity and the condition of the book, according to AbeBooks. The single most important criteria for determining the value of a book is its condition.
The criteria for determining the value of an old book always starts with the condition of the book, explains AbeBooks. An otherwise valuable book in poor condition can be worthless. After determining the condition of the book, it's important to look at the other criteria.
The age of the book is a consideration, as is the particular edition. A first edition is always going to be more valuable than subsequent editions. ARC or advanced reader copies, especially those signed by the author, are the most highly prised editions in most cases. The age of the book is not as important as the other criteria, and is often the last thing to be considered in valuing books. AbeBooks makes the point that a book is not valuable simply because it is old; it must have inherent value in the first place.
The final criteria often used to value old books is the rarity of the book. The more rare and more sought after a book is by collectors, the more value it holds.