I try to as it is a good way to save money. Mostly these days however, I prefer to do my reading on the Kindle. I have too many books and I don't want to have to store them. It is good if I can get the books I want in an electronic version. That is the best thing that I know of to save money on books really.
I do see anything wrong in buying a secondhand book as long as the content of those books are still in good condition that another person can read it and still get the same information as of a newer version of the same book. I used to borrow books from my course mates while at the university and after reading those books, I return them to the original owner, but not without making notes of what I learnt from reading those books. I bought a secondhand book once from a feeling student then for almost a 60% discount for he is set to graduate then and I must say that it was a good piece of business which I would take up again if such opportunity arises.
I buy quite a few secondhand books. Most times I'm not even looking for books, but once I enter any of the many secondhand or charity shops, I tend to make my way to the book section. Most of the shops tend to organize them according to what type of books they are, art, cooking, biography and so on. They also tend to be in good condition, many of which you can get for just £1.00 or less. The libraries are also great. I got a book recently for just £0.25. Not bad!
There are a bunch of 1-dollar books at Good-Will. They had the entire Harry Potter series for 13 dollars which is the same price as just one new book. They were in decent condition and every page was readable and that's the point of books, right? To read them so even if it's used, the main purpose is still there.
I am pretty sure that most of the books I have are Second handed merchandise. Most of my books are for my classes and if they were at full price they would cost me hundreds of dollars. Being in college and not having a job, it is not easy to get the kind of money in a short amount of time. So buying used books at a cheaper price is the best option.
I don't buy printed books these days, whether new or old. I stick on the internet for all information I need. But I see some individuals purchasing then near my locality.