most lens are well built. most seller wun deliberately sell faulty stuff.
anyway, when u buy, u test the stuff. happy w it, then buy.
anyway, even if u buy new, kanna a lemon guess wat will hapen? u bring back to the shop, listen for some crap from the salesman, put in the shop for 3 mth (they will tell u send back factory or some other crap), listen to more crap when u call and enquire, 6 mth later, when u finally gave up, and decude to get back the lens, they return u immediately (cus it has never left the shop), or the somehow get it workin, but charge u, cus not covered under warranty.
my opinion is that modern products are pretty good, wun spoil easily. but, they are not made to last too. spoil = throw.
unlike leica lens etc. but they cost maybe 10x more.