Grading Standards

In the U.S. coin field, grading abuse is still rampant despite the existence of certification services and the corpses of fleeced investors. It's never been a huge problem in the foreign coin field, and when you get to the outer reaches of exotic coinages such as I handle, it rarely comes up as an issue. However, I always urge collectors to be critical in this area, as even one grade difference can mean a serious difference in value for expensive or highly collected series.
There are no absolute standards for grading, except perhaps for circulated vs uncirculated (and Proof is a special strike, not really a grade). Rather, grading is a means of communication. You must deal with a number of sellers and make critical comparisons to learn what each seller's standards are. If you buy a coin graded VF and get a F, but at a F price, have you been cheated? Not really, and you now know to discount this dealer's grading by one step when considering future offers.
Following are my own standards for both machine-struck and cast cash coins.
Machine-Struck Coins
The "Our Env" column shows how we super-abbreviate the grade on the coin envelope.
Usual Abbreviation Our Env Name Description
Pr, Fr Pr Poor, Fair Really awful, little detail visible, or serious damage
G G Good Nearly all features visible, but barely
Vg Vg Very Good Well worn, somewhat unattractive & lacking in detail.
F F Fine Worn but not unpleasant
VF V Very Fine Sharp & attractive, but definite wear evident
EF,XF E Extra Fine Light wear
EF+ E+ Extra Fine Plus Very Light wear, usually some original lustre
AU A About Uncirculated Lightest of wear on very highest point or points; lustre
AU-UC AU Range AU to UC Confusing situation, as "AU" on our envelope indicates a range from AU to UC, not a simple "AU" grade.
UC,UNC,BU U Uncirculated,Brilliant Uncirculated No wear, no more than usual bag marks %age of lustre may be given for base-metal coins (EF+, AU, UC)
Pflk PL Prooflike May be a descriptive term for a particularly sharp UC with few or no bagmarks, or may be a special strike short of Proof quality.
Pf Pf Proof A specially-struck, brilliant, high-relief example
A, Abt, Nr A Almost,Nearly,About Nearly the specified grade (AVF, etc.)
+ + Plus High end of grade range, but not quite "almost" next grade
- - Dash Range grade (multiple specimens). Others use this to indicate midway between the two grades
/ / Slash 1. Obverse/Reverse grade   2.Abbreviation for repeated letter (E/+ = range EF toEF+)
cr. cr. Crude Crude striking method - portions of flan weakly struck, off center, etc. cr.VF may "look" Vg or F but is VF for series
Oriental Cast Cash Coins
Wear, casting quality, and minor flaws are factored in. Pre-Sung coins will rarely grade EF, and some dynasties or mints issued coins in VF or F. While struck lettering rises sharply from the coin surface, a cast Oriental character is like a mountain with a broad base and sharp peak. As it wears, the lines get thicker and the "valleys" fill in, causing a loss of interior detail. Unevenly distributed or multi-colored patina, edge irregularities, scratches, sand-holes, or rough surface will be downgraded if minor, but mentioned and not downgraded if more serious.
Cracks are now considered much more serious flaws than in the days when I graded most of my cash coins. I may have not noticed, or downgraded some coins with minor cracks rather then mentioning them, so if these bother you, be sure to check carefully when you receive the coin. Cracks do not always show up in photos.
In practice, there is little difference among VF, EF, and UC. A VF can be more attractive than a raw EF-UC still showing Mint filing scratches, and will make a better rubbing.
Patina is a matter of taste. Either a thin, even green or a dark brown are usually preferred, but for Song and earlier, crusty green or white is the norm for uncleaned coins. Let me know if you have a preference, or do not want cleaned-&-retoned coins. Crusty coins (lumpy green and/or hard soil) are noted, but not downgraded. Most crust can be removed through cleaning. A properly cleaned, neutralized, and retoned coin will be chocolate brown, much like a Penny that has lost its luster, just as the coin would have looked when it was in use. If you collect at the level of calligraphy variations, you can not avoid cleaned coins.
Abbreviation Description
Pr Attributable by someone familiar with the series.
G Heavily worn, but full exterior and some interior detail; usually attributable even by a novice.
Vg Exterior details sharp, 25+% interior detail.
F Average wear, 75+% interior detail.
VF Light wear, all details clear; well-cast; attractive patina. Mint state for some dynasties.
EF Little or no wear; very sharp casting. Mint filing scratches evident for Ch'ing dynasty.
UC EF, from a hoard that apparently did not circulate.