The Ten Commandments of Buying Used Furniture

You see a chair on the curb. It's sitting right in front of your building and it's free. Or, you're at the thrift store and spy a cheap sofa. But something holds you back. You're just. not. quite. sure. If only there were guidelines -- holy reminders if you will -- of things to keep in mind while looking at used furniture. How do you decide if it's the right thing to re-do? Or if you should run in the other direction?