While I also am against this practice, we to some degree already have a grading system. Chips are regularly listed for sale using terms such as, mint, never hit the tables and sharp edges.
This at least assures the purchaser to some degree that what he is paying for is not something you have been using to plug a hole in your shoe.
Perhaps I should refer to this as condition as opposed to grading but sometimes its difficult to seperate the two.
I would assume that setting a standard would be the most difficult. As Archie says its best to leave sleeping dogs lie.