http://en.wikipedia.org/wiki/Gold_farming
pretty wide-spread by now (most of the dollars earned data is from 8 or 9 years ago)
basically too much money is involved to stop the sellers; income is being taxed !!
besides, banning 400 (or was it 621?) accounts makes it sound like the server operator is being proactive
why should banned accounts be named? you wouldn't recognize the player(s) /rolls eyes