I'm a buyer and seller of used textbooks, and it would be quite helpful from a buyers perspective if the seller could make sure that either the 10 or 13 digit isbn is included in the detailed information about the book. All of my decision making is based on that number. Also, make notations as to whether the books is an international edition, or an instructors edition, etc... These editions are not practical or useful to the student or myself for that matter. Generally the school or faculty will not allow these to be used. Being truthful will get you alot more repeat buyers