Always get payment before the video or you're never going to see that money no matter how much you trust the person. Even regulars fuck us over sometimes.
If they're already paying with a gift card they know they're going behind the sites and everything already so they shouldn't mind paying you. If they've been "burned before" they'd want to use a site that has a kind of escrow system like ManyVids, MyGirlfund, ExtraLunchMoney... There's plenty if they're not scammers.
When your receive the gift card, load it to your account *immediately* because they can cancel the card after you get them their content.