<p>We buy nearly all books used online and then resell if they are not ones we want to keep. It has worked out cheaper than renting. </p>
<p>When we search for books we use the books ISBN number. There is website called dealoz that compares new, used, and rental prices from many websites. We are always careful to read the descriptions and have never received a wrong edition. Usually go for good or above condition and avoid any that say lots of highlighting or writing. Have had a couple of incredible bargains - one that was $100 everywhere else was described as having some water damage and was for sale for $3.99 - you could barely see the damage. We have only once had a problem in 4 years - a book that never arrived. Had to file a claim with Half.com and they refunded the money.</p>
<p>Overall I think buying used and reselling can be more cost efficient than renting.</p>