Fraud doesn't work that way.
The person using 'fake' cards are actually using stolen cards from other people (It happens waaay more than you think.)
The subscriptions are made as per normal, but then when people find out that their card is being used, they demand a backpay, which forces SE to pay back the money plus the transaction fee.
So no, RMT actually cost SE money in the long haul. To think otherwise is to be unaware about how credit transactions and credit fraud really work.
You have to look at this from a business perspective: If they've gotten this far, the fraud has already taken place. Banning them now does nothing as they'll just cycle in the next set immediately - again, doing this costs the RMT nothing as they just cycle through a back log of stolen credit cards. Not to mention, RMT rarely carry the money on the obvious accounts. Usually it's a stolen account or set of accounts with normal names kept hidden for the most part.
The best way to hit these guys is the same way that was done in FFXI - hit them in the wallets. Draw out the RMT to gather the money, trace the money to the bank, ban the account that's hoarding the money as well as the farming accounts - costing the farmers both time and money in the process.
