Book condition is an important consideration as I don't want anyone disappointed with their books condition. I break the books I sell into 3 categories: Antique, Used and Unused.
Antique books are near or over a 100 years old.
Used books are less than 100 years old.
Unused books are a special category of books. These are books I bought directly from the publishers as New books and have been in my inventory for many years unsold. They have no previous owner, are generally in new condition except for the wear of sitting on a shelf for an extended period of time. Dust jackets will be there. Some are even shrink wrapped.
Beyond this I also give the specific condition of each book that isn't new in its listing. The ratings are relative to what an average book of the same age would be. For instance a GOOD rating indicates a book of average condition. A GOOD book from 1980 will be in better condition than a GOOD book from 1850. I would expect a GOOD book from 1980 to be solid and firm with little to no loss of spine strength while I would expect a GOOD book from 1850 to be a little loose and maybe a small amount of foxing. Both normal for a book over a hundred years old.
As new means that the book is in the state that it should have been in when it left the publisher. This is the equivalent of mint condition.
Fine is "as new" but allowing for the normal effects of time on a unused book. A fine book shows no damage.
Very good describes a book that is little worn but untorn. Edges may be rough or slight foxing on pages of very old books but no major defects. Binding should be very solid on a used book but potentially a little soft on an antique book.
Good describes the condition of an average used worn book that is complete. On an antique book the covers may be faded, moderate foxing, spine may be loose but must still hold the book together.
Fair shows significant wear. Significant defects should be noted. Covers must still be attached even if weak.
Poor describes a book that has the complete text but is so damaged that it is only of interest to a buyer who seeks a reading copy.
Binding copy describes a book in which the pages or leaves are perfect, but the binding is very bad, loose, off, or non-existent. If the damage renders the text illegible then the book is not even poor.
If I see that a book is Ex-library or Book Club I will try and note it.