As for the cards there are a few methods you can implement to prevent fraud but you won't ever be able to eliminate it completely. That doesn't really matter since it's only 1/5 of the coins every airdrop, which means you'll be working hard without a big profit margin if you try a scam. Associating a card with a valid facebook account can be one option, then you move on to adding a second form of identification like a drivers license for example and you can do live giveaways as well as part of the airdrop. You get the word out directly in the heart of Montréal for exemple and get some good press coverage while doing it.