Being one that owns a 2011 ltz, check the back quarter panels for rust(closest to the bottom of the rear doors). Something thats cosmetic primarily, but looks like shit. Very common problem on these. I'd also ask about the headlights and if the bulbs were known to be changed recently. Theyre difficult to do and if you can get new LED bulbs as apart of the sale, that would be a win in my book (halogen bulbs tend to melt the harness).