Most records sold are second hand so taking note of the grading is important.

All records get a visual grading. If I think there may be a problem, I will listen to it.

All records are checked on a Technics SL1210mk2 with a standard Stanton cart and stylus fitted.

Gradings may sometimes be fine tuned by a + or - as records rarely fit exactly into the grading categories.
I will only grade a record as mint if it is sealed.
I will always try and slightly under grade as it gives everyone peace of mind.

I grade all my items according to The Rare Record Collector Guide
(Goldmine Equivalent In US) which states:

Mint

The record itself is in brand new condition with no surface marks or deterioration in sound quality.
The cover and any extra items are in perfect condition.
I will only grade a record as mint if it is sealed.

Excellent

The record shows some signs of having been played, but there is very little lessening in sound quality.
The cover and packaging might have slight wear and/or creasing.

Very Good

The record has obviously been played many times, but displays no major deterioration in sound quality, despite noticeable surface marks and the occasional light scratch.
Normal wear and tear on the cover or extra items, without any major defects is acceptable.

Good

The record has been played so much that the sound quality has noticeably deteriorated, perhaps with some distortion and mild scratches.
The cover and contents suffer from folding, scuffing of edges, spine splits, discoloration etc.

Fair

The record is still just playable but it has not been cared for properly and displays considerable surface noise, it may even jump.
The cover and contents will be torn, stained and/or defaced.

Cassette And CD Grading

As a general rule CD's and cassettes either play perfectly; in which case they are in mint condition, or they don't, in which case their value is minimal. 
Inlays and booklets of Cassettes and CD's should be graded in the same way as record covers and sleeves.