Here in Netherlands I think refurbished would be : second hand and serviced.
I think it might be so that it are used decks that they got back someway. They might (should) have serviced them and checked for malfunctions. I would also ecspect that there is some kind of waranty on them.
What type of decks are you talking about (
CDJ-400,
CDJ-1000MK3, CDJ2000 etc) ?