the fancy boarding school i went to had a monopoly on book-selling. Every year students would pay full price for textbooks in the fall and sell them back to the

the fancy boarding school i went to had a monopoly on book-selling. Every year students would pay full price for textbooks in the fall and sell them back to the bookstore for a fraction of the cost at the end of the year. I decided this was retarded and made a riskless market in textbooks at the end of my senior year by matching buyers and sellers and pocketing the spread (often >50%). I think I made like $800.