Before I get started spouttrade does NOT require the spout client etc, just a basic jar file. Basically when installed players rut click on another and if the other player accepts a trade window pops up where two players can trade items, when there both satisfied they can press esc and both type /trade accept. This would 100% stop thefts etc and can make players more confident in trading items, this could also work with buying stuff with your in game money. Trade an item and when the money is sent the player can /trade accept!
What's not to love?
P.s. I think people would benefit greatly from this seeming that a lot of players tend to trade items a lot!