And Yet, yesterday, I answered a Craigslist ad for a Canon 35-350mm L for $500. It turned out to be a local photographer I have bought from before. The lenses often sell for $1000 or more, but he saw dust in the lens, it had some minor paint dings, and he did not want to try to sell it on ebay.
Actually, the dust was on the outside of the rear element and cleaned off nicely. The lens is well used and has some tiny tick marks on the paint, but the glass is perfect.
So, you may have to kiss a lot of frogs, but there are some good deals as well.