I sell books I’ve read on eBay, half.com and amazon.com. I would like to buy books in bulk, used and new (that are good sellers), and I wondered:

1.What books sell best, making the most profit? Where do I get these books?
2.Are there other sites that are good for selling books? If so, what are they?
3.If you are a book seller, what kind of software do you use/recommend?
4.Other tips you can share about selling books.

Thank you for your input!