He's already been tagged previously for fake vouching himself, so it's not surprising that he has scammed you. His fake vouches were simply a set up for future scams, and you should have checked the feedback on his profile before you sent any sum of money to him. Admins/mods can't ban someone for scamming, which is why trust ratings are important.
Anyways, you need to realise that it is impossible for anyone to offer you legitimate Amazon gift cards for more than 20-30% off. If anyone's offering you Amazon gift cards for above those rates of discounts, they are likely to be scammers. Even if you use escrow, it won't protect you against carded AGCs, which can lead you to serious trouble.
So when you are dealing with gift card purchases, always a) ask for original purchase receipts b) use escrow and c) avoid anyone offering absurd rates.
If he is a known scammer, why isn't the marketplace moderators banning his profile/closing his thread?