its not so easy like you mentioned , you forgot to mention the big part SCAM 
Trade 50$ worth of BTC for 100$ AGC [ Scam happens 90% of the time when this rate followed ]
Result :
Your Amazon account being fucked for having invalid AGC , your 50$ BTC which you paid for that AGC fucked
So its not easy like you mentioned , it has huge potential of being scammed .
Trade 50$ worth of BTC for 100$ AGC [ Scam happens 90% of the time when this rate followed ]
Result :
Your Amazon account being fucked for having invalid AGC , your 50$ BTC which you paid for that AGC fucked
So its not easy like you mentioned , it has huge potential of being scammed .
I think there are ways this can be done, but with too much carefulness.
I have seen people trading their fiat or bitcoins for Amazon Gift Cards, but the only ones which are physical or purchased through cash or credit cards from a store. There are very less chances of getting scammed in these cases, unless you go for e-codes where possibilities are, you go first and pay and you get something which has already been used or invalid, so that's what we need to remain safe from.