This is my first build. It is very, very simple yet very effective.
This trading post is perfect for factions or plots servers.
The trading post has a nice private trading booth so N00Bs can't troll around by using an iron door and minimal redstone.
This concept is used by all my friends because it is the BEST!

This trading post only works on servers with land protection plugins otherwise you will be griefed.

Additional Notes

The material for the building can be changed. But the redstone contraptions must be the same.