What is the best workflow for a classified forum part ?
Eg when an item is sold/purchased/exchanged should it then be marked as “unlisted” or moved to a trash category?
Or are there plugins?
How to allow a user to unlist it ?
「いいね！」 1
I’d probably use discourse-solved, so that sold items get marked with a checkbox.
And put a link to your Classifieds subforum to show only the unsolved topics, like https://meta.discourse.org/c/support?solved=no
「いいね！」 6
Well, consider this plugin too:
A topic that has exhausted its function (article sold, changed or traded) can be archived by the seller (aka topic’s author).
「いいね！」 1
My plugin archives the topic. I needed the topic to be searchable (for bulk actions) … unlisted (hidden) topics cant be searched.
So people would mark topics as sold/purchased/exchanged and category moderator would bulk-move them under archive category. The easiest way if you want topics to remain present but don’t want them to stay under trade category 
「いいね！」 1
Any new functionality here in newer releases ? 
「いいね！」 1
ここに更新情報があればぜひ見たいです！「機密」カテゴリを実装できた方はいらっしゃいますか？
機密とはどういう意味ですか？
プライベートカテゴリのことですか？グループを作成し、その特定のグループのみにカテゴリへのアクセス権を付与しますか？
「いいね！」 1
つまり、アイテムの売買・交換が行われる場所に関する分類のことですが、このトピックはそのことについてです。