How to delete trade posts once the trade is complete thanks!

You do not. Topics are only closed when they violate site Rules.

You can edit your 1st post as "Complete" and leave the topic alone from there.

Can somebody fix that please

For the sake of records, we do not offer the option for users to delete posts, simply edit your first post as Southland mentioned above and inform people that your trade is over by saying something like “done” or “sold” then leave the topic be.