There is no definition ... chip density and 'dead weight' are usually what determines the grading, however every buyer is different.
It is a very good idea to get prices from as many buyers as possible, and know ahead of time how they will grade your stuff
before shipping.
One time I've had one buyer tell me I had junk grade boards ( $0.00 - $0.05 /lb ), another one tell me the boards were worth $1.45 /lb, and yet another one tell me $0.60 /lb.
I sold the same boards on Ebay for just over $8 /lb ( after shipping costs ) .
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