What would be very interesting as a plugin is the possibility that when a user removes his listing, a pop up appears asking if the item has been sold on the website or sold on other channels. If the item has been sold through the website, the seller will be given the opportunity to indicate to whom he has sold the item. These people can be selected based on the messages they exchanged on instant messaging. Also leave the option to only then rate the user based on that sale. Most websites use this including facebook marketplace and it adds value to the site. Attached is an example in effect on FB.
A lot off work for the programmer (3 plugins in one) but the plugin is very useful and the price for that is worth $100 :-)