As an addendum to this, if you are buying a gift card at less than cost price, then you are almost certainly buying a gift card which has been stolen, or bought with stolen ("carded") credit card details.
I never understood why would anybody sell thousands of giftcards at half of their value.
It's ok if you have one two codes and you have nothing to order and are just sitting there, but when you deal with thousands of dollars it's damn obvious you should use those gift cards yourself and better sell the merchandise.
If this gift card is reported as being stolen or fraudulent obtained, and you use it, you will obviously lose the value as the card, and also run the risk of losing your account. With Amazon this can also mean a permanent blacklist of your address and other accounts details (email, credit card number, etc.)
Rather than risk its more like a guarantee, I was just talking on another topic these days how Amazon has a habit of blacklisting even legit cards if they don't like the issuer and from that, I can guess what will happen if you're labeled as a fraudulent user.
Not even mentioning they have if not your real address at least the shipping address...
Really not worth it for a few bucks.