I have a few second hand decks, but mostly new ones.
Mainly because there's not a very big market for second hand decks around where I live. There are book-stores with used books, but decks are more difficult to come by.
Sometimes, through gifts and trades and strokes of luck I've run across a few but usually when I'm looking for a specific deck I cave in after a while and order one from one of my "providers". (Online bookstores or
Alida as a rule.)
If there was more of a market, and there was a greater selection of used decks available I'd absolutely have more of them though.