In a way, you're right, buying / selling accounts on this forum is not officially prohibited, but any member who gets caught up in such activity is marked with negative trust from DT members as a warning to others. But even if forum administration say that is not legal to buy / sell accounts, people will still continue to do that, and some sellers even advertise account selling in a way to say : "You can earn $xxx per week / month with this Hero / Legendary account" - something like offer in this link :
https://bitcointalksearch.org/topic/hero-account-1y-staked-address-neutral-trust-5143879