The Player Market is an Interface that allows players to buy or sell items from each other. Players cannot directly trade each other, but they can post listings of up to three different items (including multiple of each of the three items) that they want to sell for Coins. These listings are posted anonymously for other users to buy. Listings will be automatically deleted after 48 hours if there are any remaining items that haven't sold. There is currently no way for players to post listings for items they want to buy, only items that they currently have and want to sell.
One commonly traded Resource, Stardust, is typically bought and sold as Stardust Packs, for which each pack contains 1,000 Stardust. This is the only use for Stardust Packs and was primarily introduced into the game to allow Stardust to be sold for less than 1 Coin per Stardust. Stardust Packs can be created by clicking on your Stardust, and Stardust Packs will show up in the Home Tab and can be unpacked by clicking on them.
The Player Market has a Market Refresh of 30 seconds, such that new listings will only be shown and old listings that have been removed or bought will only be removed from the market list once the Refresh timer resets. This timer is NOT the same for everyone and is reset for an individual Player every time that they interact with the Market, such as buying an item or placing a new listing. Because of this, you can intentionally reset your timer and force new listings to appear by buying something cheap, such as 1 Stardust. This is often useful if someone advertises a good price in the Chat and you want the Market to refresh as quickly as possible to buy the item before anyone else.
All items that can be sold on the Market have a certain Minimium or Min Price and Maximum or Max Price, which defines that minimum or maximum price that the item can be listed for. These prices are occasionally adjusted by Moderators or Smitty as needed. They are primarily implemented to limit Alt Trading, or trading between Player accounts played by the same person, which is against the Game Rules.