Small differences can make ALL the difference to a collectible copy of a book. Sometimes these small details can be the condition of the book, but more often than not they refer to the relative age of the work, and its uniqueness.
What gives an edition some unique, collectible value? For most book collectors it will be provenance such as signatures, personal markings, letters, notes or otherwise entirely personal notes that tie the author of the work to that physical copy.
Take for example the following three examples of the phenomenally successful Frank Herbert's Dune series, first published in 1965 by Chilton press, and winner of the Hugo and Nebula World Fantasy and Sci-Fi Awards.
In a famous online auction site a first edition of the book (with its blue-green dust jacket and serif title script) is selling for only a few hundred dollars.
In the second, the fourth printing of the book (still by the same publisher, but the fourth print run edition), it is selling for almost a thousand dollars! The only difference is the presence of the author's signature, which has more than quadrupled its value to collectors.
Of course, if you manage to have a signed first true printing of the Chilton press book then your book is worth exponentially more once again: perhaps on the order of several thousand dollars.
After these unique identifiers, the collector then turns their attention to the quality of the condition of the book. In the case of Dune First ed., we would be looking for the blue-green, water-colour image on the front cover to be the clearest and fresh as possible, and with its characteristic circular map of the planet Arrakis on the back to be as legible as possible. Sometimes with collectible books, it is a case of how rare and against-the-odds this copy is for it to become collectible!
Herbert, Frank. Survival and the Atom. Santa Rosa Press Democrat,California (1952). Collection of articles; Limited to 750 copies
Herbert, Frank. The Dragon in the Sea. Doubleday, New York (1956). Author's first novel
Herbert, Frank. The Dragon in the Sea.. Gollancz, London. (1960). First UK Edition
Campbells, John W. (editor). Analog: Science Fact and Fiction. Conde Nast, New York (1963). first publication of Frank Herbert's 'Dune'; complete set 8 volumes- Dec 1963-Feb 1864 and Jan – May 1865; Includes 'Dune World' and 'Prophets of Dune'
Herbert, Frank. Dune. Ace Books, New York (1965). Cover art by John Schoenherr
Herbert, Frank. Dune. Chilton, Phildelphia (1965). First book in the 'Dune' series; book club edition and trade edition; Cover art by John Schoenherr; First issue dust jackets have 4 lines of publisher information, subsequent copies have 2
Herbert, Frank. Dune. Gollancz, London (1966). First UK Edition
Herbert, Frank. Dune. Chilton Book Company, Philadelphia (1968). Second printing
Herbert, Frank. Dune Messiah. G. P. Putnams Sons, New York (1969). 2nd book in 'Dune' series; Book Club Edition and trade edition
Herbert, Frank. Children of Dune. Berkley Publishing Corp., New York (1976). 3rd book in 'Dune' series; multiple printings in first edition
Herbert, Frank. The Dosadi Experiment. Putnam, New York (1977). DJ by Paul Alexander
Herbert,Frank. The Great Dune Trilogy. Victor Gollancz, London (1979). Dune Trilogy: Dune, Dune Messiah, Children of Dune
Herbert, Frank. God Emperor of Dune. G.P. Putnams Sons, New York (1981). 4th book in Dune series; Edition includes a limited edition of 750 copies signed by author
Herbert, Frank. The White Plague. Putnam, New York (1982). First trade edition
Herbert, Frank. Dune. G. P. Putnams Sons, New York (1984). 25th anniversary edition
Herbert, Frank. Heretics of Dune. G. P. Putnams Sons, New York (1984). Limited Edition of 1500 numbered copies signed by author; 5th book in 'Dune' series
Vinge, Joan D. The Dune Storybook.. G.P. Putnams Sons, New York (1984). Based on the novel by Frank Herbert; Adapted from the screenplay by David Lynch; illustrated with stills from the movie
Herbert, Frank. Chapter House Dune. Gollancz, London (1985). First UK Edition; 6th book in the 'Dune' series
Herbert, Frank. Dune. Easton Press, Norwalk, Connecticut (1987). Memorial Edition; Illustrated by John Schoenherr; plus 1 map; includes 20 pages of personal stories from various authors, including: Poul Anderson, Isaac Asimov, Ben Bova, Ray Bradbury, Charles N. Brown, F. N. Busby, Harlan Ellison, Philip Jose Farmer, James Gunn, Joe Halderman, David G. Hartwell, Peter Israel, Willis E. McNelly, Frederik Pohl, and Jack Vance.