I have bought and sold about 800 books on eBay (about 650 sold, and 150 bought), and it is still probably the single best place to get a wide chess-playing audience for your books that are for sale.
The real issue is if your books are really any good. I bought two books from eBay that I am waiting for right now: One is just a book that is near-and-dear to my heart, that is a first edition hardcover from 1964 in like-new condition, and the other is a very coveted book by Igor Khenkin about checkmating patterns in like-new condition. The problem is that most of what I see on eBay is junk, often in fair condition at best, and then on top of that, it is overpriced.
If your books are in nice condition, and somewhat valuable (search sold listings on eBay to get an idea what it is really worth, and also used listings on Amazon, although they are prices from dealers, so a bit high, but they can still give you an idea if is is a $10 book or a $200 book, or worthless), then it can be worth it to sell them individually.
If you have a bunch of old Dover or Tartan books that were mass produced, then they are not going to be worth much. Typically, these were cheaply made, and thus, they did not wear well over time. You need to realize that they might only be worth a couple of bucks each, and thus, you should bundle them, and price them accordingly. There are a lot of people out there with these books trying to sell them, so there is a lot of competition, so price will be king.
One last factor is the material in the books, and this relates to the age of the books. Today's books are better than ever, and much better at teaching, so not only will they be in better condition since they are newer, but they will have more coveted material. They will be worth more. Opening books do not age well unless they explain well, and are aimed at mid-level players, rather than cutting-edge analysis.
Craigslist is just a step up from yard sale prices, and unless your books are those junk books to be sold in lots, I would not recommend it for selling collectible, or any decent book.