I have been playing games since 2014 and selling game currency since 2016, never heard players' accounts got banned because they bought currency. For example, if NCSOFT bans Gold buyers, most of the players already got banned, for there are millions of players have been bought Gold, in this case the game BNS should have died already. For NCSOFT’s another game Blade And Soul, a player who talked about this ban case said that "I knew a number of people who bought Blade And Soul Goldand never even received a warning about it unless they talked about it openly/bought very large quantities."