Your going to need to show proof of how these are obtained otherwise no one will bite. This section is full of scams.
Thanks for a wise remark. I've included a screen with my account with gift cards, hope it adds some trust. Anyway, I'm all for escrow if the buyer insists. Even can do escrow up until the client uses the gift card for stays at hotel/other services (since it is very easy to check whether the card was used, when and for what service). You can sum up any amount using these cards and you will also get you rewards points for using these cards.