Edition does most of the work
Buyback value is overwhelmingly a function of whether courses are still assigning your exact edition. A current edition of a widely required text is a genuinely liquid asset. The previous edition of the same book is often worth a fraction of that, and an edition two cycles old is frequently worth nothing at all to a vendor.
This is why the ISBN matters so much. Two books with identical titles and nearly identical covers can have completely different buyback values if one is the ninth edition and the other the tenth.
Demand, which mostly means enrolment
A book assigned to 2,000 students a year in general chemistry has steady, predictable resale demand. A monograph used in one seminar of twelve students does not, however excellent it is. Introductory science, maths, psychology and economics texts hold value best, because the courses are large and the books are expensive new.
Condition, within limits
Most vendors expect used textbooks to look used. Moderate highlighting and a creased cover are normally fine at the standard price. What actually costs you money is structural damage — a split spine, loose or missing pages, water damage, or heavy marking that makes the text hard to read. Those can mean a reduced offer or rejection once the vendor inspects the book.
A practical note: sell the book with any dust jacket and supplementary CD if it came with one, since some vendors check.
Things that are usually worth nothing
Consumables. Workbooks, lab manuals and anything with pages you filled in have no resale market.
Used access codes. Single-use by design, so worthless once activated. Their absence does not usually hurt the book's own value.
Custom campus editions. Books bundled specifically for one university often cannot be resold anywhere else.
International editions. Many US vendors decline them outright. See our guide on international and older editions.
How to actually check
Find the ISBN above the barcode on the back cover, and enter it into a comparison tool that queries multiple vendors at once. You will usually see a spread rather than a single number — that spread is the point, since the highest and lowest offers for the same book on the same day are often far apart.
Check during finals week rather than later. As the timing guide explains, the same book is typically worth more in May than in July.