Haha I knew this will result in a post of you.
Ehm you know that those RMT sites have to get MP/GR cards first, before they can sell it? They can't create them. It has nothing to do with RMT, the cards are already ingame, not because of them.
Maybe they bot in GD/Gr maps too.
It works like that:
1. bots farming cards(very easy on iRO)
2. bots vend cards(very easy on iRO)
3. get billions of zeny(very easy on iRO)
4. Buy MP/GR cards from other people by offering a very good price(they dont care for zeny)
5. Selling MP/GR for USD is much easier than selling zeny.
Or do you want to tell me that iRO has a exploit to create mini boss cards or MVP like tao gunka? Afaik is or was tao gunka on iRO camped by bot for long time.