Once you trade an item, it's gone from your inventory. It does not return unless you trade back for it.

This has nothing to do with TF2Outpost though as the site does not hold your items.

Since there is no API to directly retrieve an item's history from Valve, there's no guarantee that this info is accurate. A new owner will only show up in the list when their backpack is scanned by the site. The easiest way to do this is by viewing their inventory through the site.

You'll probably receive a faster response if you submit a support ticket on the site.

https://steamhost.cn/steamcommunity_com/groups/tf2outpost/discussions/0/558747922562007365/#c540742485382301536

This is unrelated to: http://www.tf2outpost.com/

https://steamhost.cn/steamcommunity_com/groups/tf2outpost/discussions/0/558747922562007365/#c540742485382239358

https://steamhost.cn/steamcommunity_com/groups/tf2outpost/discussions/0/558747922562007365/#c540742485382266453

Please read this: https://steamhost.cn/steamcommunity_com/groups/tf2outpost/discussions/0/558747922562007365/#c540742485382239358

Unless you have no intention of selling the item you have, it still is a trade.

The forum is not a place to post trades. Create one on the site and wait for offers.