Duke's system best.
At 10€ the game, a tard golden boy could easely fraud if he really want and then just re-sell the accounts at 7-8€.
Duke's system means spent time to share with community, only truly motivated troll could pass that.
Wikipedia use a system a bit alike Duke's system, result 95% of the obvious troll aren't enought determined to pursue, 4,9% pass but get caught few time later (few hours/days/weeks), the last 0,1% are the subtil/disguised troll and the true problem. It take month of investigations to demasked them ; they are like determined terrorrist you can't do anything but watch them and waiting a suspect behaviour until they blow themselves somewhere where it causes lot of damage.
If some vicious peoples I met over there could make a donation to freely fucked up Wikipedia, trust me, they'll do it. It'll same here.
Duke's system have the advantage to test their patiences, asked them to be wise during a time, and that it's really hard for troll, more than put 50$ in system to fuck it up.