To some people $400 dollars is nothing. If they want to buy a beta account with it, more power to them. At least they will play and test the game. As far as the people selling them, although it's wrong we don't know the circumstances behind it. Maybe they needed the money to buy food, pay the rent, fix a car, or maybe they are just greedy.
Money rules the world. Nothing can be done to stop it, and it doesn't ruin my fun, so whatever. I know I liked the money I got for my FFXI account when I quit. At least I didn't completely waste my time.