That shows the lens has taken a hard fall or been knocked heavily against something. The damage to the exterior housing wouldn't worry me so long as it can still mount a filter and hood. But I'd be concerned about the interior bits... it won't necessarily show up as something rattling inside or be something that can be seen by looking at the glass... But there can be decentered elements inside a lens that's had a hard bump, effecting every image made with it. It would have to be a great deal for me to consider it. I'd want to take a bunch of test shots to be sure it's still working properly. I try to keep it in reasonably good shape, but don't worry very much about the cosmetics, just about the performance of my gear.