This is meant to be a quick and dirty method for evaluating raw Standing Liberty Quarters. It's worked well for me, and I find that it pretty well corresponds with roughly what a TPG would put on a coin, aside from the odd market graded piece although you're only likely to see that in these dates on a 1927-S, particularly in higher circulated grades.
These coins are outrageously overgraded out there, this should give you a basic fighting chance.
The 1925-1930 is the most common date range out there, mainly because the dates on them were recessed, so they stuck around with legible dates for much longer and people held on to them, as opposed to the 1917-1924 Type 2 coins which are prone to severe date wear. I used, with the exception of the AG coin, all 1928s here as the dies are largely the same, most are 1928-Ss. Remember that these coins have the odd issue with strike quality too
About Good:
Obverse: Date is still largely clear and readable, rim is worn away and top edges of "LIBERTY" are worn away. Motto may be worn to where it's tough to read, same for the stars.
Reverse: Rim is long gone, letting and stars wearing into what was the rim, only the outline of Eagle's feathers to be identified.
Good:
Obverse: The rim is still worn away, but the tops of "LIBERTY" aren't eaten away. Drapery is still visible at the top of Liberty's left leg. Areas of her torso above hips still rounded.
Reverse: Well worn, however some feather detail remains on leading edge of Eagle's wing, Eagle's right inner wing shows numerous detailed feathers.
Very Good:
Obverse: Rim is defined but some letters in "LIBERTY" are just a hair from touching or barely touching the rim. Liberty's eye on her head should just show, drapery on her left leg should be defined.
Reverse: You should see a full defined rim even if weak. Eagle's right wing should show inner feathers from very nearly the top of the rim down to the breast.
Fine:
Obverse: The line at the top of Liberty's right leg is clearly defined and the left leg has no flat spot breaking the drapery at the knee. No part of the date touches the rim, you can just make out the nose on Liberty's face. The quickest visual check for me is to look for a small triangle of cleavage on liberty's chest.
Reverse: No part of the lettering touched the rim which is sharp and well defined, feathers on Eagle's right wing are virtually all there except for the leading edge.
Very Fine:
Obverse: Shield is outlined fully and not worn into Liberty. Also, Liberty's sash is clearly defined and not worn into her. Liberty's chest is, well the right one is defined while her right leg is still flat.
Reverse: Feathers on right inner wing show detail all the way to the breast of the Eagle, rim is clearly higher than edge lettering.
Extremely Fine:
Obverse: Liberty's right leg shows most knee definition, the lower part is rounded still. The chain mail of her top is clearly defined above her chest and below the neck. Shield is fully outlined, most of inner ring of shield is outlined. Design on inner edge of rim virtually all there.
Reverse: Easiest check is that the Eagle's LEFT wing shows most feather detail, wear on the leading edge of the left wing only. Right wing is sharp.
I hope this helps, comments, criticism, corrections, etc are all welcome