My wife purchased her Janome 9400 as a demo machine, trading in her 6600. She saved $1000 over what she would of paid by trading in her 6600 on a new machine.
That machine has had enough quirks, even after having it back for service once, that I think we would of bought new if we did it again.
That said, we've bought lots of used things over the years that have worked out great.
Jim