Look for business directories online by searching for "Singapore business directory" or look around your house for a business phone book. In the directory, look up businesses that buy and sell second-hand books in your area.
Call the businesses and ask them if they accept the particular textbooks you want to sell, and how much they would pay for the books. The Bras Basah Complex near the City Hall MRT Station features many used book stores that might want to buy your textbooks, so you can try visiting them to make inquiries.
Go to the book store with your textbooks to exchange them for money.
