Here you will find a basic example of conditions that I use to grade most common portable typewriters. Rare/Unique/Scarce or Office model machines are graded differently.
Mint Condition:A mint condition typewriter is defined by The Vintage Typewriter Shoppe as being 99% perfect or better. A mint condition typewriter will have near perfect decals, nickel, paint and be in like new working condition. There may be no signs of use and simply minor scuffs from being stored. The enamel and plating will be bright. The machine will have been disassembled, degreased, cleaned, oiled, adjusted and come with a new ribbon. The condition of the decals is extremely important to the value of any vintage or antique typewriter. Watch out for typewriters that have silver decals when they should be gold. This usually means the gold was washed off by a cleaning solution at some point. The Corona Four pictured is in mint condition. All the decals (including the rear panel decal) were near perfect and it showed only a little wear from storage. The nickel and scarce green and gold finish is near perfect and original.
Near Mint Condition:A Near Mint condition typewriter is defined by The Vintage Typewriter Shoppe as being 98% perfect or better. A Near Mint condition typewriter may have minor finish loss to decals, light scratches to nickel or some minor paint scuffs on the finish but still be in near perfect working condition. The signs of wear will be minimal and far less than normal wear for it's age. Most buyers have a difficult time seeing the difference between near mint and mint. The machine will have been degreased, cleaned, oiled, adjusted and come with a new ribbon. The flaws in this LC Smith Corona are decal damage on the rear panel from being removed from the base and some minor finish loss to the paper table decal. The nickel and gloss maroon finish are near perfect and original.
Excellent Condition:An Excellent condition typewriter is defined by The Vintage Typewriter Shoppe as being 95% perfect or better. An Excellent condition typewriter will show far less than normal wear but visible signs of use are common. There may be a chip or scuff on the front of the machine or partial decal loss (usually on the rear panel) but will still be in near perfect working condition. These are still considered collectible but can be used on a regular basis with less concern about decreasing the value. The condition of these typewriters are well above most that you find for sale online or elsewhere. The machine will have been degreased, cleaned, oiled, adjusted and come with a new ribbon. The areas on this Olympia that fall into the "Excellent" definition are several chips to the paint in normal areas. The chrome is bright in most areas and still very presentable. Again these are still fine machines with desirable original cosmetic appeal.
Very Good, Good, Fair and Poor refer mainly to cases. I will use Good and Very Good for Bargain Basement machines. They refer to the overall cosmetic condition. Mechanically, BB machines are just as functional as investment grade machines.