The vast majority of their books are listed as "NEW-Has Remainder Mark" (small black marker slash on the bottom of the book near the spine). The description of each book will tell you the condition of the book, so please read those carefully.
Right now, they're offering FREE Media Mail Shipping for any $15 or more order (sales tax only in MA). They also accept PayPal, or you can use Visa/Mastercard through their regular checkout.
Very nice selection, and excellent prices. I ordered quite a few of the "Magic School Bus" series of books, and they're $5.99 each at Amazon, but they were $1.50-$2.00 each at Sort Floor Books. Be advised that this site doesn't have information on the content of the books. I just searched Amazon for the ISBN# to check reviews, price compare, age group, etc.
Also, if you have items in your cart but you're not ready to place an order yet, make sure you click the "Save Shopping Cart" button (or your items will not be saved).
FYI...All orders are sold on a non-returnable, non-refundable basis. For more information please read their return policy:
Edited to add...I just placed my order around 3AM this morning, and I already received my SHIPPING confirmation email from them...very fast!
Received my shipment and was very pleased. All books were new and in excellent condition, only one had an actual 'remainder mark'.
(Big thank you to Ennadee over at MC)