I got this idea from Owen and he said that Plots should have a /sell and that command sells the item in the players hand and I think that may be a good addition to Plots or and all the other servers.
Maybe just Plots. Survival doesn't have a server/admin shop, therefore it would be a little peculiar to have the ability to sell stuff infinitely. Plots, on the other hand, has a server shop. However, if this plugin is added, the server shop has their OWN prices, so some changes will probably be neccesary. Creative would just be stupid to have /sell, and KitPvP might be cool.