Well, I probably annoy people by repeatedly mentioning this but…
There are the ToS everyone agrees to when playing the game.
And in these ToS there is this part:
2 General Terms and Conditions: The whole use of Services, including Applications within Services, shall be governed by the following terms.
2.1.3 Accurate and Secret Information: You shall provide Tacticsoft only with accurate information about yourself and shall keep Your User Account information, including password and other login information in utmost secrecy and shall be liable to any damage, direct or indirect arising from the misuse of Your User Account. Should You find that any personal information regarding Your User Account has been violated or disclosed, You shall immediately and without any delay (1) notify Tacticsoft of any unauthorized use of Your password and User Account; and (2) make intentional efforts to ensure that no other party misuses Your User Account thereafter.
Point 2.1.3 already prohibits giving other people your account info.
As such “trading accounts” is also prohibited by this part of the ToS.
Even more so it mentions that you are liable for any damages caused from your user account if you have not informed TS immediately in case you find out that it was used by others or that its login information has become known to others.
So anyone who “trades” their accounts is directly responsible for any misconduct the new user of that account does.