I've found AbeBooks to be the best, although obviously it's not local. But it's a better resource--so long as you know what book you want--to get various versions of old books. It even tells you what condition it'll be in so you can be sure to grab a nice version if it's a special very favorite book for your collection.
I do know that small booksellers use AbeBooks to sell. So while it's not necessarily YOUR small and local, you're still sometimes buying from small booksellers and supporting them.