Here is the thing about Gil sellers.
Square Enix is a business. Like all businesses they are in it for the money, nothing more. They, like all other MMO RPG’s like to say how they disapprove of them yada yada yada. They will however to appease the masses ban the level one character and that account. But they do not ban the ones that are actually selling and farming for the sellers. This is because they posses many accounts that are being payed for and thus they are making money from said accounts. This allows them to basically burn the candle at both ends. They get to look like they take a hard line against RMT while at the same time making money from it.

If a company truly wanted to remove RMTs from their game they could. This is a few of the ways that they could;

1: When they kill the account of the level 1 character they could also ban all accounts connected to the IP address
2: All accounts attached to the MAC address
3: All accounts attached to the billing (address, credit card Ect.

Basically we will never be rid of them in games because both they and the company make money off of us.