Yes! I have bought almost everything used or demo from a dealer. The biggest thing was my turntable. I paid less than half retail for the complete setup. Table / arm / cart. And he setup everything up for me.
A good dealer will stand behind the things they sell. So if there is a problem, they will usually take care of it. I have been happy with everything I have purchased used or demo. And by buying used or demo, the piece is already broken in.