I've been able to clean-up my used 3rd Gens & blend in (out?) any scratches or wear marks to my liking. I believe with some judicious use of Scotchbrite pads you can make that scratch almost disappear.
If you're going to use it as a shooter I wouldn't let that scratch be a deterrent.
Use the "no box, paperwork and only one mag with yellow follower" as bargaining chips to get them to lower the price. Can't hurt.
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