Reasons for trading restrictions :
1) Steam Guard Not Enabled or Recently Enabled
Steam Guard (via email or mobile authenticator) need to be enabled for 15 days. If you have not had Steam Guard enabled for 15 days, you will be unable to trade or use the Community Market. Accounts that currently have Steam Guard disabled will be unable to trade and use the Community Market.
If you have recently enabled Steam Guard via email on your account, you will be unable to use the Community Market for the 15 days after Steam Guard was enabled. Removing Steam Guard or disabling and re-enabling Steam Guard will also trigger this restriction.
2) Password Reset Recently
If you forget your password and need to reset it (note: this is different than changing your password), you will be restricted from trading and the Community Market for 5 days. If your account has not had any activity for more than two months, these restrictions will apply for 30 days.
You can change your password from the settings panel in the Steam Client. This restriction only applies to password resets, ex: done via https://help.steampowered.com or by Steam Support.
3) Newly Authorized Device
If you are logging onto Steam from a device that has not been previously authorized by Steam Guard (log in confirmed via email), you will not be able to trade or use the Community Market from this device for 7 days. Any other devices that have already been authorized for at least 7 days will still be able to trade and use the Community Market.
Actions such as clearing your web browser cookies, using a new web browser, reinstalling Steam, and reformatting your computer will make that device look new to Steam and will trigger this restriction.
Exceptions: If you have had a Steam Guard Mobile Authenticator on your account for at least 7 days, there will be no trading or Market restrictions for using new devices/computers. This is because you'll confirm trades and Market listings from the mobile app.
4) Community Ban
You also may be unable to trade or use the market if your account has been banned from trading by Steam Support. Depending on the severity of the violation, you may receive a temporary or permanent trade ban.
5) Mobile Authenticator Added or Removed
Adding an authenticator does not immediately remove existing restrictions. Trades created within the first 7 days of adding the authenticator will still have up to a 15 day trade hold.
If your account was already protected by Steam Guard via email, you will have no new restrictions from using trading or the Community Market. If your account was not protected by Steam Guard via email or mobile app, you will be restricted from using trading and the Community Market for 15 days because Steam Guard has been recently enabled.
Removing a Steam Guard Mobile Authenticator reduces your account security. To help protect your items, you will be unable to trade or use the Community Market for 15 days.
6) Other
· Changing your account email address will restrict trading for 5 days.
· If you choose to cancel any of your accepted trades that are in a trade hold, your account will be restricted from trading for 7 days for your protection.
· Items purchased in-game or on the Community Market will not be tradable or marketable until after the date indicated on the item in your Inventory.