The attributes affecting the grading of a card include the condition of the corners, the edges and the surface, the color on the card, and how well the picture is centered and focused on the card. The condition of the card back is important, too, although it may not matter as much to a particular collector.
Vintage cards (those printed prior to 1980) may be graded somewhat less strictly than newer cards, although I don't know of any official rule about that. Vintage cards, even when new out of the pack, were widely subject to printing flaws of all kinds: color imperfections, centering problems and out-of-focus picture.
Here is a summary of the grading guidelines.
Grade | What to look for |
---|---|
Mint (MT) | Basically the card is perfect. Centering is nearly 50-50, corners and edges are smooth and sharp, and there are no printing imperfections. |
Near Mint-Mint (NRMT-MT) | Centering is at least 60-40 with smooth edges. May have one small flaw such as one slightly worn corner or a minor print imperfection (print spot, color imperfection). |
Near Mint (NRMT) | Centering at least 70-30. One minor flaw such as: two or three slightly worn corners, slightly rough edges, or minor print imperfections. |
Excellent-Mint (EXMT) | Centering at least 80-20. May have two minor flaws such as those listed under Near Mint. |
Excellent (EX) | Centering at least 80-20. May have four rough corners and minor print imperfections. |
Very Good (VG) | Corners may be slightly rounded, edges may be rough. Gloss and color may be somewhat lost. May have tiny creases. |
Good (G), Fair (F), Poor (P) | These have obviously seen hard times. Very well-worn. Serious creases and discoloration. |
Professional grading companies use different scales. PSA, for example, grades on a scale from 10, which they call "Gem Mint", down to 1. BGS uses a similar scale.