From my knowledge, this is how a Middle Man can help.
Don't flame me if I'm wrong please
Person A has 50K NX and Person B has a 1LT account.
They want to exchange via Middle Man.
Person A and B add the MiddleMan on Messenger.
Person B will give the middleman their account login and pass change info, and the middleman will change the pass.
Then Person A will give their NX codes to the Middleman.
Then the Middleman will give the NX to Peron B.
person B will report whether it works or not.
If it does, the middleman will then turn over the account login/info to Person A.
If it doesn't, the middleman will tell Person B the password they set so they can login and change it back to their choice, and Person A will get a warning/ban for giving a fradulent NX Code.