I usually buy used to save cash. Got most of my lenses that way, including one (Sigma 14mm) from the USA (KEH.com). The only abject failure that I had experienced was on a new lens (AND new camera) that I purchased back in 2007: both broke within a month of each other (and within 4 months of purchase). The important exclusion is the Canon 24/1.4 L lens that I bought new two years ago - and it's not seeing a lot of use. My current 16-35 workhorse (the f/4 IS) is a cross between the two: I bought it from a guy found on the Internet but the lens was brand new in box with complete package. All the others - including my second workhorse unit, the 70-200/2.8 L IS - are/were second hand.
Actually, scratch that - the horrible Konica Minolta 18-70mm kit zoom was also new when I bought it with a KM camera way back in 2006. I sold it for peanuts shortly after getting a couple of proper lenses to cover that range - and it was bought by someone only because he needed to cannibalize the mount and electronics for a tinkering project of some sort. I can sympathize with that because the junk like that lens has no real right to exist anyway.
Actually, scratch that - the horrible Konica Minolta 18-70mm kit zoom was also new when I bought it with a KM camera way back in 2006. I sold it for peanuts shortly after getting a couple of proper lenses to cover that range - and it was bought by someone only because he needed to cannibalize the mount and electronics for a tinkering project of some sort. I can sympathize with that because the junk like that lens has no real right to exist anyway.