Trading

The trade window. The direct trade window stays. You can trade items, orbs, runes and gold. Both sides see every item's full tooltip, with affixes and values, and both must confirm twice: once to make the offer, and once more on a final screen that shows the other side's contents. The trade is one transaction: it either completes entirely or not at all.

Rules (the level, hub, gold-cap and logging rules are coming soon; the window itself works)

Both characters must be level 10 or higher, in the same hub, and not in a map or an instance.
You cannot trade with another character of the same account. (The account stash shares items among your own characters.)
Gold received cannot take the receiver above the gold cap (coming soon; The gold cap).
Maps and unidentified items are tradeable as they are.
A trade with an item that cannot be shown is refused.
Every trade is logged on both sides.

Not tradeable: quest items; Writs and Seals; trial maps; season-only consumables; tutorial items; the Flask Belt (Pinnacles and Writs, Seals and the Sigil of the Unburied King, Ascendancy trials).

Finding buyers. Players trade directly or advertise in the public trade chat channel. Link your item so that buyers can read it (Item links in chat).

Prices. Players set the rates; one Chaos Orb is a common unit of account, with Exalted and Divine Orbs as larger units (The orb economy).

Safety. Check the tooltip and the second confirmation screen. A link shows an item as it was when linked, not as it is now, so verify in the trade window (Item link limits).

Later: a trade site (coming soon). A listing fee of 1% of the price (at least 100 gold) and a 2% sale tax, both burned, will make trading a modest sink. The gold cap may rise then.