Real money trade is the act of using real money to purchase virtual in game money. This is a frowned upon offense, as well as bannable. It is specifically state in the Terms of Service that you are not allowed to purchase or sell any of your gold/armor/characters for real money (of any kind). The effect on the virtual economy goes far. It can drive prices up or down for items.
Some of the businesses that actually sell gold/armor/characters use bots, or farmers to gather the gold. Farmers are often underpayed, work long hours, and live in poor conditions. Supporting a Real-Money Trade business is not only ruining the game, but is also supporting what is basically a sweat shop.