The team of Navyfield and sdenternet say :

<<Dear Community,

After circumspect consideration, we decided to disable trade completely (Area 13 + trade system) at the End of May 2017.Trade had caused serious problems in the past and we spent many working hours on resolving these, especially with the large number of players sharing their accounts and got their crew hacked. Our current policy is that TeamNF do not involve in trades and you should be responsible for what happens on your account if you share it. However, we try to be kind and don't want to upset our players sometimes even it's their careless act they should be responsible on their own. Unfortunately these cases are non-stop happening and with trade enabled it's also hard to stop event exploiting with multiple accounts.  We allow you to play with multiple accounts on single computer/IP now but event exploiting is still prohibited. Also, on some other MMO games, there are no trade system and all run without any issues. >>

Why don't keep your promises ?

If you look at all the top online multiplayer games a trade system is at the heart of many of these games without exaggerating. Removing the trade system is creating a even bigger gap within the online community as well as restricting and crippling the players in what we can do in the game.
There are always going to be hackers/scams in every game and I blame the naivety of players who do get scammed for not doing their research before undergoing trades