As the title suggests, there is no way to safely and securely trade items.  There is an official trading forum, which is encouraged by the devs, yet there is no way to allow a safe trade.  

Someone can drop ingots or what ever into an unlocked box for the trade, the other party can simply lock the box and be off without completing the trade.  Worse yet, some random can find the unlocked box and steal the contents.

And what happens then?  There's less than a snowball's chance in hell of WC support actually doing anything about this.

Thanks.

I didn't find the right solution from the internet.
References:

• https://survivetheark.com/index.php?/forums/topic/156809-no-way-to-safely-trade/
• Animated Explainer Videos Examples