Yes, if you take the time and if you are experienced in looking at Ebay adverts for lenses (or anything for that matter on ebay) then you know what to look for and what the red flags are. The only time I didn't go to ebay was when I wanted an authentic grip for my D800 and was tired of looking through hundreds of ebay ads for grips claiming to be genuine Nikon grips (even with fake Nikon boxes, etc.). At that point I'd rather pay extra for the real thing. Otherwise, if I can save literally hundreds (or even thousands) of dollars on slightly used equipment, why not? Imagine what more then you can buy with that money you save? More lenses? Or even to trade up later. I bought my D700 on Ebay and saved hundreds off new and it was literally like new. I even sold it for more than I paid for it, again on Ebay.
There's always risk when you buy something, but that can be said even when you buy something new under warranty. If one doesn't want to spend the time to research the possibilities for good deals, and is happy with new or refurbished, then I can understand that. Personally, I enjoy shopping for camera stuff and part of that enjoyment is doing the research into what is the best deal for the best item with the best value. I've even waited for prices to come down on things second hand just to be able to afford the kinds of things I like to try out. It is incredible these days the resources we have available to us online. I remember when I shopped for cameras back in the early 80s and then I was just visiting the local camera supplier in a department store (remember that? Certain department stores used to have full camera outlets with specialists on hand to help you choose the right equipment), and took home all the brochures/catalogs I could carry to study the specs. In another 30 years I'll be sending out orders for camera equipment directly from my brain to a mainframe computer LOL.