Imagine a tab like this where we could send all the items that we want to trade.
We would add any and all tradable items here and set an initial price that we want for them before engaging in any trading, be it platinum or any items or mods. This would also remove said item from our normal inventory so we wouldn't sell it for ducat or credits accidentally.
Players would then be able to set up shop at Maroo's in a similar form to Baro as seen above where other players could interact with us and see our "shop".
Additionally, players could share a link to their trading tab in chat so people could see the items that are up for trading from there and if they found something they want then they could invite each other and trade in person.
The actual trading process would still be the same so for example the number of tradable items per day would limited by the mastery rank of the player. and the "price" of the item would be editable.
For negotiation purposes both sides would still have the ability to change the details of what is being traded. So for example if you set the price of an item to 10 plat in your shop the buyer can still select it and during checkout you or the buyer could suggest a new price for any of the items (set it to ammo drum for example), just as is the case now.