Oh..... I think u mean you were selling.... That 2 lens should never sell..... They are damn good!
Well, for lens, better buy new....
A. Second hand price and new price, not that much different, (especially canon, used price here, is higher then new price from HK sometimes)
B. Unlike bodies, hard to chase how many pictures were taken...
C. You can hardly tell how how a lens was used, while optic/glasses can check, but the motor (usm ) can't. In general speaking, usm from canon is reliable, but not sigma/nikon etc are not. (early nikon afs)
Some lens I wouldn't mind to buy is 'kit' lens, I bought off the 18-135/15-85/55-250 etc kit lens from my friends brand new.
They are better then before .. but instead of use to be 1/3 the price compare to "Factory" lens, now they are 2/3 .. or more as the 50mm F1.4
I still prefer the Canon 50 1.4 and Nikon 50 1.4 more then the sigma ... as they are much ligher, faster focus, no af issue, less distortion ... less $ ( somehow ) and more "factory" colour. (as I don't PP much .. old school )
But give credit to the sigma one, the Bokeh is great, quiet, and sharp. (once on focus) It still much lighter then the 50 1.2. ^_^
On the other hand, somce Tokina/Tamron are great for you buck .. 12-24 .. 11-16 .. 17-50 .. 90 .. etc ..
From experience, Canon lens hold better value than other third party lens...
On crop body zoom lens, for sure it's the 17-55 f2.8 IS la... even if it's a bit expensive and plastic feel. However, in terms of photo quality, focus accuracy, colour, bokeh, etc. all outbid others.