@alexfw
Obviously, the more items which you list, the greater potential for sales.
And the secret is to offer books which very few (if any) other booksellers are offering -- all "best sellers" from the last 35 years are too thickly abundant; and, unless you have a Near Fine (or better), first printing in dust jacket edition, there is little point in adding yet another lesser graded listing to the multitudes which are currently available.
Better to concentrate on esoteric pre-1990 titles, with shorter press runs, that may not have been "best sellers" in their time, but which have gained interest over the years.
Additionally, pre-1990 non-fiction titles seem to be good "long term" investments, as well as movie, music and TV tie-ins from that same pre-1990 time period.
With my books, I am not concerned with immediate sales (although they happen with a very satisfying regularity); but what I am counting on are the "spur of the moment" buyers, who have been spent years searching for a particular book, or author, or subject matter -- and who finally discover it on my site, where it may have been sitting for years, just waiting for the right buyer.
And, the more similar titles which you list, the greater the chance of attracting more and more of those "spur of the moment" book hunters.
Most of the really good antiquarian book sellers whom I've met over the past 60 years have had one very good quality in common -- the patience to wait for a book to be sold to the right buyer.
Good luck!
