It seems that ISBNs have been out only since the 70s, which means that most truly valuable books won't have them.
I almost did a web dev job for a bookseller who was closing his bricks-and-mortar store to go online, and he said the really profitable books were not the really old ones. It would be a book someone remembered from their childhood, etc. Mostly modern stuff. It takes a seriously long time for oldness to impart value.
I almost did a web dev job for a bookseller who was closing his bricks-and-mortar store to go online, and he said the really profitable books were not the really old ones. It would be a book someone remembered from their childhood, etc. Mostly modern stuff. It takes a seriously long time for oldness to impart value.