1. Best lens I ever used for general wide to short tele. I've had many others bought and sold incl 18-55 IS, 17-895 USM, sigma 17-70 etc I had rented the 15-85 and the 24-105 L together, took a lot of shots, could barely tell the difference in IQ, so I got the 15-85 to save a few $$ and I wanted the shorter end of the zoom.
Very good build for a non-L, despite reviews I have seen no CA, yes, some vignetting which is automatically removed in processing, very sharp, etc etc
It's not my money, but I would fork over a few extra bucks if you can to get a new one rather than a used one.
I know it's a lot, but today, lenses are not just glass , they have moving parts(IS, AF) etc. I would only buy a used lens from a reputable dealer who tests and checks out lenses. Not that an individual seller would be out to stick you w/a lemon, it's just that he/she might not be aware of the true condition of the lens.