Same as getting a 2nd opinion from a doctor. Why should a card be penalized because it is in the wrong holder? People focus on the flip and not on the card. If you sell a card that is in a holder lower than it deserves to be in, then you lose money, as bidders will focus on the low grade and pay the low grade price. You would be better off cracking the card out and selling it raw!
Case in point....no way would I be happy selling this card as a '4', as it looks like a '6'......it deserves '6' money.