There are many book sellers in each city, and they are very keen to purchase the old and used JEE books, as there is a very huge demand for second hand books for JEE Main and Advanced, given the expensive nature of these books. So, if you live anywhere in or around Delhi, you can go to Kalu Sarai and you'll find a lot of book sellers who will be ready to give you a handsome amount for your books!

Hope I have answered your question. All the best!