You should actually stop shooting arrows blindly.If he can prove with valid sources that the card obtained is legally ,he is free to exchange it for btc .How can it be pretty clear to you that the card obtained would be illegal ? I got a mail from one of the Shopping Website's I usually shop from that they're giving me a Gift Card worth $50 and I can use it before end of this month.Obviously if I'm not interested in buying anything at the moment I would not want to card to be wasted but to be sold by taking a small loss (not even a loss since I had it for free).I know this can't be the same case every time but you should validate stuff before posting a conclusion.