Before you create your own listing for each book, do a thorough search for existing listing pages. You do not want to junk up the catalog (any more than it already is) by creating a new listing for a book that already has an existing page. Plus, it will be easier to find an existing page in a search. Be sure to check title, publisher, publishing date and edition. Many pre-ISBN books have multiple pages and it can be hard to determine where to list your copy. If you have doubts, ask. There are still plenty of experienced old-time book sellers on here who will help you out. I, for one, would rather help a new seller list a book properly than have you make mistakes and suffer insurmountable consequences.

Keep in mind, not all old/rare books are valuable. Not all old/rare books are good reads. There are plenty of poorly written, sucky old books as there are poorly written, sucky newer books. Just think, in 100 years, Dean Koontz books will be old and possibly rare, but they will still be bad books (my personal opinion, of course; others may happen to like his writing).

If you have some true gems in your collection, you may want to check out other bookselling venues such as Alibris or Abe Books. These are sites that book collectors would search before coming to Amazon. If you do not want to list on those sites, at least visit there to see how your tomes are listed (condition/price point). You will get a better sense of what your books may be worth over there. Keep in mind, book buyers who really want an older book are going to do their homework and look for the best copy at the best price no matter the site.

When you do decide to list them, be sure to provide a very detailed description in the condition notes. Re-iterate the edition and printing, if necessary. Old books have flaws and buyers want to know what they are. Some buyers don't mind if a book has a broken spine or dog-eared pages. Others will steer clear of books that have water damage or markings.

Read and note to memory the condition guidelines for each grade. If in doubt, grade one level down. Old books that are in acceptable condition with good descriptions can sell better than higher graded books with little or no descriptions. Case in point, I recently sold a pretty pricey book in acceptable condition at a higher price point than others listed in better condition. I honestly believe it was because I listed every issue with the book. It was old, the cover was damaged, the spine was broken. But I beat out a generically-described very good copy at a lower price.

Finally, as previously mention, it may take a while for your rare books to sell. This will not be a get-rich-quick endeavor for you. It may take years. The previous book I mention had been in my inventory for about 15 years. I almost gave up on it a few times and thought no one would ever buy it. When I first listed it the ranking was about 5M. When it sold it was about 12M in ranking.

Good luck!