As someone who has run large book stores and small, it's all about the people - those behind the counter and those searching the shelves. Nowhere else in retail can you experience that kind of interaction between customers and employees.

Seriously, you don't work in a used bookstore unless you love books. You don't go to a used bookstore unless you love books. Therefore, you're in a place you love surrounded by people who love the things you do. That's a positive place to be.