scratch

"natural" silver aluminum, or Space gray or some other color?

Aluminum scratches can be buffed out with mild abrasive such as Automotive buffing compound. They will look less obvious when buffed.

Repairing Space Gray or other anodized colors is very difficult. For Space Gray, you could use a sharpie marker to cover it and expect to re-apply from time-to-time.

Leave the scratches alone. You will make it worse by trying to repair them. Look at them as indicators of use and experience. Your computer is a tool not something to sit on a shelf looking pristine.

Even silver MBPs have a clear anodized coating. It is what give the case that "slick" feel.

Sanding/buffing will remove the rest of the coating and the aluminm will start to darken.

Pretty much anything you try will make it look worse.

Only if you are willing to spend a lot of money to get it back to "showroom" condition. The cost for changing major body components is quite high. For example to replace the cover over the screen requires the entire screen be replaced, around US$650 for the 13-in model.

Consider selling it "as is" to someone who is not fussy about scratches. You MUST divulge any defects you know about including scratches. To not do so is Fraud.

You can ask Apple (we are not Apple) but I have never heard of Apple making out-of warranty cosmetic repairs. They replace parts.

As Grant has already said, the display on a Retina Macbook Pro is one unitl and must be replaced as such ar a horribly high cost. The replacement would be cheaper if it is a non-Retina MacBook Pro but the only one of those Apple still classes as "supported" for parts and service is the 2012 13-inch Model (model identifier MacBookPro9,2).

You could try emery paper, spit and elbow grease. YMMV.