RMT spammers just create tons of new characters on one account, deleting old characters as they go. On my server, you don't get tells from the same person more than once, so blacklist options do not help. And no, you can't stop RMT in a game of this nature, you can only limit the damage the abusive behavior causes.

The only way to prevent the type of spam we currently experience is to have moderators taking immediate action against accounts that are being reported for spamming. A brief glimpse at the /tells coming from the account, and a gm should immediately lock the account BEFORE an investigation. Accounts cost RMT spammers at least $15-$20, so getting the entire account locked after one wave of spam would make it impossible to profit from randomly targeted spam. That would effectively remove these /tells from the game.