- Pristine mint: Knives in this category must be flawless, and must have additional characteristics that set them apart from mint. They could have an unusually good fit for example.
- Mint: This would be a knife that has never been carried, never sharpened, never used, and does not have rust problems of any kind. Some collectors will classify a very old knife that has a few rust marks as mint (especially those made prior to WWII). The newer the knife gets from there, the less rust specs it must have to maintain its mint status. In addition, most Case knife collectors are a bit stricter on grading knives. An old Case knife with any rust mark would not be considered mint. Note: A knife that had rust, and was cleaned to look mint would be considered near mint or worse depending on how harshly it was cleaned.
- Near Mint: There must be nothing wrong with a near mint knife. It should walk and talk and must have most of the original polish visible on the blades. Very light sharpening would be acceptable, but the blades must be full. It can have some light rust spots, but no deep rust pits. Some light carry scratches are permitted on the outside as well.
- Excellent: Knives in this condition would include solid, lightly used knives. There may be a bit of blade wear (no more than 10%). Some tarnish and light pitting would be acceptable. Blades should snap well, and the tang mark should be clear. Very Good: Knives in this category are generally fairly well used knives. There may be blade wear of up to 25%. The blades should still be sound, but one or more may be slow. The stamping should be readable, but may be faint. The handles may have cracks and wear, but shouldn’t have major chipping. The knife might also have some rust pitting and tarnish.
- Good: Knives in good condition must still be useable as a working knife. Blade wear may be between 25-50%. There might be chips in the handle or blade. Blades may be slow with deep pits and rust. You should still be able to make out the maker of the knife by shield or tang stamp.
- Poor: A poor knife is generally only good for parts. The blades might be less than 50%, extra lazy or even broken. Tang marks are generally barely legible, and the handles may be chipped. Junk: Anything less than poor. These knives would be pretty much worthless. May have a liner, back spring or bolster that would be salvageable for parts, but probably not even that.
Source: All About Pocket Knives