i was searching for a used MacBook Pro and the 2017 models were all heavily worn down. I’m talking scuffs, scratches , dings, etc. I can see a 2013 being in bad shape but a 2 year old MacBook being in that kind of shape is terrifying.
You could go to Apple's refurbished pages, and save some money on a 2017 model.
You might even find 2015 15" MBPro's available from time to time (they come and go quickly).
If I needed a fresh MBP, I'd probably look for an Apple-refurb 2015.
The "last good design", in my opinion.
Others will disagree.
That is human nature. You will have people who take great care of everything they own, others who take care of nothing they own a lot who fall somewhere in between. Like they may treat their computer with kid gloves, but not care all that much about their car or truck.
Some of what you are seeing may also be previous business machines and in some cases when people don't pay for or own the machine themselves, care might not be as important.
Notebooks are tools to be used, not precious objects. We all want the best, equally if wanting some pristine experience purchase new and vacuum seal it. A few scuffs and scratches will save a good deal of money, nor impact performance...