My grading scale is as follows-
    M - Indicates that my copy is a master tape. Letter grade is A unless otherwise indicated.
    S - Indicates that my copy is SVHS. Will also include a letter grade rating.
    A - Excelent quality. Picture is clear, with no color bleeding. Audio is clearly audible.
    B - Fair quality. Maybe some color bleeding or other video problems, but subtitles are easily readable. Audio track may have minor static or hiss.
    C - Poor quality. Major color bleeding or static. Subtitles may be dificult to read in places, but are mostly readable. Audio may have major static or hiss, but is still mostly understandable.
    D - Horrible quality. Subtitles are dificult to read in most parts. The audio track may be dificult to hear through the static.
    F - Unwatchable. It may be dificult to even tell what the picture is supposed to be in most parts, and the audio track is probobly mostly inaudible.
    +/- indicates a title that is particularly good or bad for it's grade, but not enough so to push it into the next grade.

I generally don't distribute tapes where my copy is below a C letter grade. And I wouldn't reccomend requesting anything in the C range unless you are desperate and can't find it anywhere else, or just don't care about quality.