Trade-O-Mat

This very awesome block can sell as well as buy items

Usage
Simply put a itemstack of your choice into the marked (left, with the lock symbol) input slot and another itemstack into the output one. Then place a Chest (or Personal Chest, to protect your money) nearby and fill it the same item the Trade-O-Mat is configured to output. They no longer need to be equal in number.

Any player (including yourself), can drop items into the public input slot (on the right). It will then be added to the chest, and the output will be taken from the chest and placed in the output slot.