Very tricky question to answer. I think it all depends on individual. Some people surf the B&S for weeks to get a good deal 2nd hand lens (w/o warranty) overlooking the fact that a brand-new grey set probably costs the same.
Just an example, I've a friend who had been looking high & low for a Sigma 10-20 and was so happy that someone finally offered to sell at $700. The very same day, we paid a visit to Orient Photo & found that the brand new grey set costs $720.