I have never sold my textbooks. During all the time I spent at school, I never took a class that involved books I wouldn't want after the class finished. I kept all of them, and probably still have them somewhere to this day, except those that were left at the house on Stirling Street and carted away by the person I hired to take and sell the leavings of that place.
However, my son has no such feelings about his books. Not a book or reading person to begin with, college classes hold for him none of the wonder they held for me. I had always hated high school, where I was taunted and tortured outside the classroom and distained within its doors. Teachers didn't have time to deal with someone as different from the norm as I. Sometimes my differences certainly presented challenges for the teachers, as with my math disability. It was easier for them to assume I was stupid, ignoring my performance in English and history, and to let me quickly sink to the bottom and drown in those classes. In English, the teachers often assumed that the work I was doing was plagiarized, and said as much to me. No one with the lack of brains they believed I had could do the work I was turning in. I think about that when I want to accuse someone of plagiarism. I need fairly solid proof that it was not done by the student.
But my son told me to pack up and sell his books, so not having any experience in this department, I went to Amazon and learned how to sell them. I looked up the going price for the books, and listed them. In 5 minutes, one of them was sold. It took overnight to sell the other two. We will use the proceedings to pay for his algebra book, which costs $179.00 new and $117. used.