Auction, aka the Auction House, is where players can trade with each other
Auction is located on an abandoned cargo ship in Southeast Salvation Town. Talk to the Auctioneer Cecile to enter the Auction menu.

In Auction, most transactions cost island coins.
Players can browse and purchase a variety of items that other players put up for sale, including weapons, backpacks, tools, gears, materials, consumables, recipes, mounts etc.

On the Sell tab, you can choose items from your backpack or storage crates and put them up for sale.

When doing so, you can specify the amount and the listed price of an item.

The item will typically be listed for 2 days, and it will be sent back to your mailbox automatically if it is not sold in time.