These are the classifications that I use to grade the new and used CDs I sell on eBay.
I try and avoid selling CDs in less than Very Good condition.
Both the compact disc and the front liner notes are graded separately in the auction listings.
As I can't listen to each one in their entirety, the grading is based primarily on a visual basis.
I will not sell any CD that appears to be unplayable.

Jewel cases may occasionally be cracked or have a sawcut, drill hole or some other minor damage,
indicating that the CD may be a promotional item or a factory return.
Some cases may be cracked, or have a broken hinge.
In these cases, I'll note the condition of the jewel case in the description,
but please keep in mind that I am not grading the jewel case, as that is not the item being sold.

Sealed CDs are literally still factory shrink-wrapped in plastic -
typically, including the top adhesive label with the artist and album title.

The CD and the liner should both be in mint condition, as it has never been opened or played.

Mint CDs are just that, mint.
This means they should appear as if you just removed the
shrink wrap and opened the CD for the first time.
There should be no wear around the spindle hole or marks to the playing surface.

A Mint condition liner should be in perfect condition with no creases, folds, dings or wear.

Near Mint CDs are those that have been gently and carefully played and stored,
but show some small signs of wear. There may be some minor wear around the spindle,
or scattered small fine marks from finger prints, dust and normal handling.

A Near Mint front liner may have some evidence of use but is not creased or damaged.
It may have indentations (but should not be torn) from the plastic jewel case tabs,
when the cases were closed with the liner on the wrong side of the tab.

Very Good condition CDs are those that have obviously been used but not abused.
The CD may have fine surface scratches, minor wear around the spindle hole,
or more significant marks on the non-playing portion of the disc.

As CDs play from the inside out (the opposite of vinyl records),
CDs with shorter playing times might not have any data in the outer 1/2-inch
to 3/4-inch region of the disc. Scratches in that area should not affect
the play of the CD, as the laser does not track this portion of the disc.

Very Good condition liners have normal wear but do not have any major defects.
The damage from the jewel case tabs may be more severe,
and cut or torn the paper in the front liner.