As non-fiction/fiction book categories are so generalized in terms of time period covered (and signed/rare pretty general too) I would like to suggest the following to encourage more rare book dealers to list:
Books>Antiquarian>pre-1850>Fiction
Books>Antiquarian>pre-1850>Non-fiction
Books>Antiquarian>1850-1900>Fiction
Books>Antiquarian>1850-1900>Non-fiction
This would be a great help for people who deal primarily with antiquarian books, versus the new and "used" books listed in the standard book categories.
Either that or another setup could be (as signed/rare alone is too big a bucket):
Books>Signed & Rare>pre-1850>Fiction/Non-Fiction
Books>Signed & Rare>1850-1900>Fiction/Non-Fiction
Books>Signed & Rare>post-1900>Fiction/Non-Fiction
It would even be better to replace "rare" with "antiquarian," as "rare" is pretty vague.
My suggestions are just to look at creating the kinds of categories that would attract buyers and sellers of rare, collectible, and antiquarian books. There are really two groups of books on any auction site: Books for readers (standard fiction/non-fiction, new or used, but generally recent) and books for collectors (who are looking at specific topics and time periods). As a buyer and seller of the latter, I woud love to be able to hone in on those books of interest, without having to wade through a large pool of reading copies.
Thanks, RebekB at Coelacanth Books