Most of the sites have member reviews, which can help you pick out ones you want.
My experience with these sites has been 99% positive, and the people on them are usually very quick to fix problems if there happens to be any. 85% of the children's hardcovers I've received have been ex-library, but not falling apart.
If you list books, make sure that you list them by the ISBN number. Make sure that your book comes out as the format it really is (Hardcover, Paperback, Library Bound hardcover, etc). Nothing sucks worse then getting a paperback when you want a hardcover (at least to me, ha ha). You can help stop this problem by double checking. This problem usually occurs when someone has to look inside of their book for the ISBN and there are multiple ones in there (or if your book is a book club book). Here are some hints: "Lib Bdg" = Library Binding (AKA Library Bound Hardcover), "Pbk" = Paperback, "Trade" can mean regular hardcover and in some cases paperback. Most of the sites get their listing information from Amazon, and sometimes Amazon is WRONG. All of the sites let you enter a book from scratch if you run into these problems.
Your choice of books is only limited by what other people are willing to send out. The biggest downside is that you have to go to the post office and pay to ship your books out to people. Shipping to you is free though!
My three favorite are listed below, including some of their good and bad points:
Paperback Swap :
An AWESOME site with MILLIONS of books:
A) 2 free credits after listing 10 books.
B) You earn credits by having your books requested, but you do not get the credit until you send the book and the other person receives it and marks it as received. This kinda sucks if things get lost, but if you pay for shipping + delivery confirmation + $0.50 through the site you can get your credit right away.
C) PaperbackSwap has strict condition rules (must list under proper ISBN, book must not be falling apart, no water damage, no teeth marks, etc).
D) It is first-in-first-out. If you are the first person to list a book, your book will be the first to be asked for.
E) They have a "no swapping to sell" rule that they claim to be able to hunt you down if you try (ha ha). They will cancel your membership if they catch you.
F) One big downside, they allow hardcovers to be Dust-jacket-less, and there is no way to know if the book you are going to get will have one or not because they don't have condition notes (if you are ordering a hardcover). I have had many "dang it" moments, but I have also had many woo-hoo moments too!
G) All orders are supposed to be sent within 1 week of being ordered. I usually get my books faster through PaperbackSwap because of this.
H) You Can BUY credits for $3.50 each (plus a total fee of $0.50 is added to your order… I am guessing to cover some of their credit card and/or PayPal costs) if you run across a book you must have but don't have credit for it! This is NICE, but spendy. If you join their SwapaDVD site (http://www.swapaDVD.com) you can trade DVD credits for Book credits (2 DVD credits for 3 book credits)
F) You can make "Requester's Conditions" requirements like "NO Smoke smelly books" that a person will have to comply with before sending you their copy of a book. If you receive something that doesn't fit your requirements, you can get your credit back (and recycle or give that smelly book to charity).
G) They have a wish list and they will email you and hold the book for a couple days for you to order it (limited to 200 titles currently, and the first person to "Wish" for a book will get first option to order it).
H) You can give other credits.
I) OVER 3.7 million books to choose from!
J) Free to join, free to be a member (for now)
(Logo artwork courtesy of BookMooch.com)
A GREAT site with ove a million books from all over the WORLD:
A) 1 free credit for EVERY 10 books listed (1/10 of a credit per book) (list 100 books, get 10 free credits).
B) You earn 1/10 of a credit by marking a book received (receive 100 books, get 10 free credits).
C) You immediately get a credit when someone asks for your books (10 books requested = 10 credits)
D) You can get Books from other countries! They cost an extra credit, but there are probably some great books out there that aren't in your country!
E) You immediately get a credit when someone asks for your books.
F) You can't buy credits on BookMooch.
G) There are optional condition notes. It is always great when you can read that a book comes from a smoke free home and is in brand new condition.
H) You can request any book you want based on condition notes. In other words, if 75 people have the book you want, you get to pick and choose which person you want to "mooch" from.
I) People can take as long as they want to send your book… I waited over 6 months for one, but that was an extreme case. A lot of people on a budget only send out books once a month up to a certain dollar amount, and they tell you that on their page.
J) They have a wish list. Bookmooch will just send you an email when someone lists a book, and then you have to hope that you are the first person to the site to order it. One nice thing about the list is that it is unlimited.
K) You can give credits to others.
L) Pretty much advertisement free
M) Over 1 million books to choose from!
N) Free to join, free to be a member
Frugal Reader http://www.FrugalReader.com
Not the best but certainly not the worst:
A) List at least 9 books, and get TWO free credits. Once someone receives your book(s) you will get your credit(s)
B) You can become a "Premium Member" after two of your books are requested and received (there are some perks for this).
C) You can buy credits for $2.99 to $3.49 each (depending on how many you buy at a time).
D) Not as popular as Book Mooch or Paperback Swap. So, the selection is lacking.
E) People can set their books to cost more then 1 credit, and hardcovers are usually 2 credits. So, someone can "jack-up" their "prices" for current popular books, or be nice and keep them at 1 or 2 credits. I have seen a hardcover that I really wanted on there for 6 credits ($17.94), but I refused to pay that.
F) There is a wish list.
G) People can list condition information
H) Some annoying advertisements.
I) Over 29,000 books to choose from
J) Free to Join, free to be a member
There are other companies out there, but these are the main three for me. Some of the others are linked below. Feel free to tell me about others, please!
NOW, GO OUT AND DO SOME BOOK SWAPPING!
Recycle your books and get new-to-you ones!
http://www.swapsimple.com/ (not just books, but $2 fee per trade, ugh)
http://www.readitswapit.co.uk (UK swapping site, so, I've never used it)
http://www.swapadvd.com (great DVD swapping site, connected to PaperbackSwap)