I never buy used unless I know the original owner (aka, a good friend of mine). The only exception to that is if it's something that I can't live without, that's really hard to find new (collectibles, etc... ). Not that there's anything wrong with used, I just prefer buying new.
I would buy used if I found the right deal, but it seems like the way most guns hold their value and how people are willing to pay top dollar might as well buy new if not saving much.