It all depends…

Is it a factory original boxed gun? Like other Pre-64 guns, there are fake boxed M12s circulating with phony end labels.

Then, there are guns there were used (or handled a lot) that were put back in boxes, sometimes not their own.

Obviously, these guns should sell for much less than genuine NIB guns.

To me, a NIB gun should be in new condition, as should the box, and all the tags and papers should be included. Ditto for brown waxed paper, spacers, etc. I have seen "NIB" guns with a ratty boxes and no contents except the gun priced at a premium as if they were complete and excellent condition. Why buy one of those?

As to prices, be prepared to pay a lot for a NIB gun that is what it should be–they are rare and rightly high priced.