I believe this plugin could be useful for many servers, as it utilizes a GUI to allow players to sell any item. This is preferable over other selling plugins because other plugins either use villagers (which take up too much space and aren't useful for multiple items) or signs (which take up too much space and are hard to organize if you want to sell any item).
This plugin has a simple file to edit prices and you are even able to ban the selling of certain items if you wish. It also has an option to sell custom items, which not many other plugins have.
This plugin would be very useful for my server and many others, here is a link to the site: https://www.spigotmc.org/resources/sellgui.55201/