This is a money-making proposition that's not for everyone, and won't make a fortune - but done well, can bring in a few dollars for the emergency fund.

You'd need someone with these qualifications:
            Knows and likes books of all categories
            Has a great deal of spare time (or at least an hour a day, on average, plus time to attend sales and frequent establishments)
            Is computer literate and has access to the Internet

In a nutshell, this person (or persons) will buy books cheaply, post them to an Internet auction that specializes in media, and mail them to the buyers.  The money can be deposited directly into your organization's account, or whichever account you wish.

In detail, it goes like this:

Most Internet junkies are familiar with the popular auction site called Ebay.  Ebay has an affiliate site called Half.com, which specializes in selling books, videos, CDs, computer programs and more.  We're interested in the books; if you want to spread out to include the other areas, you'll need to read up on the procedures for those.  Unlike most auctions, you set the price for your books - no bidding or haggling.   Suggested prices are given, and you can view what other people are selling the same book for. 

If this peaks your interest, go to the site and look it over.  That's www.half.com.  Read in particular the "selling your stuff" section.

Now - about finding the books to sell.  You have plenty of choices:
Auctions:  Estate or household or consignment; you can find them by boxes or individual, and often for pennies a book.
Garage sales:  Same situation as auctions, only you haggle instead of bid.
Library sales:  Okay, this is a deeper subject.  The ideal is to become a member of a local Friends of the Library that allows their members to sort all year long and buy books for set prices.  Their regular sales, especially in larger cities, are usually spectacular displays of bookdom, and you can clean up.  Some libraries have ongoing sales set up in their facilities, and you should haunt those frequently.
Colleges:  Higher education texts are in demand simply because they're so expensive new.  Ask around at your local college or university about where they keep the used texts.

Probably the most important thing to learn about this venture is what kind of books to buy.  At first, it'll be a learning experience, even for people who think they know books.  Here're some tips:
The general public won't pay much more than a couple of dollars at best for a hardback fiction book unless it's an unusual one, such as a popular first edition, or a signed copy, etc.  The paperback ones are practically worthless to mess with.  If you want to bother with the hardbacks - storage and packing costs and time - that's fine.  This is just a suggestion.
To make life easier, stay with the newer books, the ones that use an ISBN number or UPC code, or both.  Older, or vintage, ones are saleable but probably better sold through a place such as Amazon.com (they have an antique book section) or some other site that specializes in such.  With the older ones, as well, you'll need to list with photographs of the book since anyone seeking that category will want to see what it looks like.

Some categories that are popular at auction are collectibles (reference and general information), genealogy, crafts, up-to-date computer books, up-to-date self help, historical interest,

Ebay offers some success with books, but my experience leans toward half.com and Amazon.com.  Your experience may shed a different light.
Book Selling Online