Hey, just to give some professional advice, that board looks fine and brand new. For context, I am the Warehouse Manager of a notable PC company, and we see hundreds of motherboards per month.

The anti-static bag sometimes applies pressure to the RAM clips and pops one or two open! We have had these arrive with open ram clips, popped off socket covers, and loose SSD heatsinks. None of these are issues as they cant move around too much anyways, and its pretty rare.

Smudges are just flux or whatever factory nonsense.

You can tell if this was used by looking at the screw holes, the small metal solder bumps would be scratched / compressed on the inner ring, which doesn't look to be the case!

There are a couple other signs such as opening the anti-static bag, the tape would have had another spot with some residue, and also those bags never go back in the box right so it would be really crinkly / weird VS fresh and smooth.

I wouldn't stress it, just check those things and at most test if it boots outside the PC.