My kids rented all of their’s from Cheggs.
I remember paying something like $75 for an Econ book in the early 80’s and getting $3 back when I resold it.
College students don't need to be told that books can be found online. They've been shopping online their whole lives. My youngest child started college in 2003. She bought some books online. At the time, a bookstore, I think Barnes and Noble, had a deal where if they didn't have a book in stock, they'd order it for you, and if it didn't arrive within three days, you'd get it for free. She figured if she bought the book at B&N instead of the college bookstore, she at least had a shot at getting it free.
My daughter discovered that on her own. Why was she looking for bargains? We told her we'd pay her college tuition and room and board, but her books and spending money were her responsibility. She worked summers to earn money for books and spending money and earned some money at college babysitting for one of her professors.