Looking at an 07 Chevy Cobalt- the price is good, mileage low, and AutoCheck through Experian checks out fine- no accidents, no rental use, etc.

Only thing that concerns me is that there is no Chevy emblem on the trunk lid, and it doesn't say "Cobalt LS" like other models do. Why would this be??

It's possible that the trunk lid needed repainting: scratched or dented.
It's possible these minor trim items were inadvertently omitted during it's build.
It's possible they were removed for visual asthetics.
Have you asked the seller?