Selling Sold

Alright first of all, leaving this thread open instead of deleting it is done to keep track of transactions. Not just for him, but if people accuse him of something etc. then the moderators can help out.
Secondly, you have absolutely no reason to attack anyone in the community for leaving a thread open. The thread is assigned to have its item sold as seen by the title. That is enough indication and hence no further steps have to be taken.

Edit: It is a common thing for people to have 1 single thread they keep editing if they sell items so they have everything together. Same applies to buying threads or even shops.