We make every effort to fill your order as requested, but we reserve the right to make substitutions if your books are not available in the requested condition. This means if you select "used preferred" and a used book is not available at the time your order is filled, a new book will automatically be substituted, and vice versa. The dollar amount of your order WILL change if substitutions are made. All prices are subject to change without notice. Please note: while both used and new prices may be listed, this does not guarantee the availability of textbooks in these conditions.