There's a nice essay by James Grippando M.J. Rose's blog. I second the emotion: If you buy books, PLEASE buy new if you can. Writers make zero dollars from used books. That's zero dollars as in: Zip. Nada. $0.00. Not-one-thin-dime. If writers don't make money, then the publishers don't make money. And if publishers don't make money, they won't publish any books. And readers won't have new books to read.
If you love to read; if you care about books, words, and the marvelous way in which books feed our imaginations, then please, buy new if you can. If you can't, that's okay! Check out books from your library. Libraries are funded in part based on numbers of patrons. The more patrons, the bigger the budget. And libraries are the bedrock (along with good manners) of civilization.
So please, if you can possibly do so, buy books new. If you can't, then please, patronize your local library. We'll all be better for it. Thanks for stopping by. Thanks for reading!