I've bought probably 50+ used lenses and camera bodies and have yet to have a problem. (As a SELLER I've had 3-4 problem customers out of maybe 120 sales.) I would not consider buying new equipment, usually, though of my current outfit I did get the 100-500 and 135/1.8 new. Even if it's only saving 10-20%, that may cut the total cost of ownership (purchase price minus sale price) in half. And if you want gear that's not sold new, used is basically the only option. I think it's worth considering.