Buying new books online is pretty easy–we all just head off to Amazon (or Book Depository, or Waterstones, or whatever) and fire off our order. But you should definitely consider buying second-hand books instead. For one, they're invariably cheaper. And for another, it's better for the environment.

It can be a little harder to find them online, especially when you can't see pictures and have to worry about things like quality. So, here's a guide to five of the best websites you can use to source your second-hand books, and how to ensure you're getting exactly what you want.

1. eBay

Results page on eBay for Harry Potter books

eBay has absolutely got to be the first port of call for anyone looking to purchase second-hand books. It has a vast range of titles, especially for those which are more popular, and you can often find them cheaper on here than elsewhere. Also, you're very likely to be familiar with how it works already, including checking seller ratings and sorting by price.

In general, there should be enough sellers on eBay offering the books at a fixed price that you don't need to resort to bidding. Bantam Books and CMedia are two of the best known sellers on there, but there are a whole host of others.

Many offer multi-buy discounts, which allow you to save a percentage if you purchase several books in one go from the same seller. Using this, you should be able to fit in four or even five books for between $10 and $15—something that would be impossible if you were buying them new.

The only negative to eBay, which is true to some extent for all the platforms on this list, is that you're heavily dependent on the seller to correctly categorize the book's quality. Is it "Like New", "Very Good", "Good", or merely "Acceptable"?

No matter how trustworthy the seller, misplaced expectations are a real concern. Since the seller will rarely bother to upload actual images of the book, using stock images instead, it's really anyone's guess how the book will ultimately turn out.

Also, try not to set your heart on specific covers. When collecting a series, many people are keen on ensuring the spines are all lovely and matching, but trying to get the cover you want requires matching bibliographic data for specific editions (and even then, it doesn't always work). You may not care so much about this, but it's certainly something to consider if all the other books you own in a series are from a specific print run.

On the whole, though, buying second-hand books from eBay is cheap, fast, and reliable.

2. AbeBooks

AbeBooks Homepage

One of the most popular second-hand books sites out there, AbeBooks, is dedicated to matching sellers with buyers. It can occasionally be pricier than eBay, so it's always good to compare first, but it has a nicer user interface.

Many independent booksellers use this platform, so it's a good way to support them too. Unlike on eBay, where it's almost completely up to the seller what details about the book they want to include, almost all AbeBooks listings come with a good number of bibliographic details—including the all-important book condition, binding, and publisher.

AbeBooks has a particularly good focus on textbooks and rare or collectible books. While we don't imagine that many of you are looking to purchase a first edition of EM Forster's Passage to India, which recently went for over $18,000, you can find plenty of signed books on here.

Meanwhile, AbeBooks also has its own podcast, Behind the Bookshelves, which covers a range of literary topics.

3. ThriftBooks

ThriftBooks Home Page

ThriftBooks is especially fantastic for getting a great deal on books that are no longer in print, and might be ridiculously expensive elsewhere. This is all because of its excellent email-notification setup.

If you sign up to be notified when a book you want is in stock, you'll be emailed instantly as soon as it's added to the site. This way, you'll often be able to snap up cheaper copies of books which might be more expensive elsewhere, so we can't recommend the site enough when looking for a rarer book.

There are a couple of other pros to shopping at ThriftBooks too. For instance, it has a ReadingRewards system which lets you earn points on your purchases (eight points per dollar spent), which can then be redeemed on books. There are also multi-buy offers on some books.

If you're interested in selling your second-hand books, ThriftBooks also happens to be one of the apps on this list of the best apps on which to sell old books.

4. Better World Books

Better World Books Homepage

Like World of Books, one gigantic upside to Better World Books is that it offers free shipping on all books, no minimum purchase amount required. That holds true, no matter where you live, but the price of a book does change to reflect built-in costs. For instance, a copy of Kresley Cole's fantasy romance novel A Hunger Like No Other (located in Indiana) is about $10 when coming to the UK, but only half that when being shipped within the US.

BWB also sells new books, which is why it appears on this list of the best Amazon alternatives for buying books. However, its offering of second-hand books is where it shines.

We're impressed at its efficient, easy-to-handle search functionality, as well as the range of titles on display. Like ThriftBooks, there's a multi-buy discount which lets you save 15% when buying four books (a percentage that rises the more books you buy in one go).

Also like ThriftBooks, there's a rewards program which lets you earn eight points per dollar spent. When you hit 500 points (or about $63) you'll be entitled to a $5 voucher.

5. Alibris

Alibris Homepage

While Alibris occasionally has good finds, it's last on this list for a reason. First of all, it doesn't automatically offer free shipping: only some books are eligible, and even then, you have to order $39 worth of books. It also doesn't automatically add the shipping cost to the book cost, so you don't immediately see the real price of buying a book.

That's not to say Alibris doesn't have its plus points. For one, signing up to its newsletter gets you a $5 discount code. For another, it has a lot of ways to filter search results. You can sort by price, condition, release date, and even how far away from you the seller is located.

Speaking of sellers, it has the eBay-like feature of a seller rating. They're ranked and starred, and even have Seller Storefronts, where you can check out reviews from other customers.

Meeting Your Second-Hand Book Needs

The five websites we've listed above should be able to get you absolutely every second-hand book you've ever wanted to read. Between them, eBay, AbeBooks, ThriftBooks, BWB and Alibris have millions of titles on offer.

Buying second-hand may mean yellowed pages and the odd bent cover, but it'll free up your budget for tons of new books—and that's the really important thing.