Anyway, It really is simple
How to USE the chests
Basically all you do is right-click (or place block) on the trade sign with the payment (second line) in your hand.
If you get the message: Items exchanged, They might be invisible. Then the trade was successful, If you don't see the items, just click in the first empty space in your inventory and they will appear.
If you get the message: This chest does not contain <#> <Item>. Then, its out of stock you cant trade, I'd suggest using /msg or /mail to notify the seller.
If you get the message: You do not have <#> <Item>. Then you don't have the payment, and you cant buy.
If you get the message: The chest is full. Then the seller overstocked, I'd suggest using /msg or /mail to notify them.
If you get the message: There's not enough room in your inventory. Then, you need to empty your inventory some so you can trade.
How to MAKE the chests
Step 1: Private the chest. Do this by right-clicking it with a sign.
Step 2: Shift+click (or sneak+click if you've changed controls) a sign on the chest
Step 3: Type like this:
Line 1: [Trade]
Line 2: <#> <Item> *This is the price*
Line 3: Doesn't matter what you put
Line 4: <#> <Item> *Item Sold*
Do not put in the "<>" or "*...*"
Step 4: If you did it correctly, then your good :D
Common mistakes
1. shows in chat: You need to protect the chest first
Fix: Private the chest. All chests need a private sign on them, even if they're already private from another chest. Do this by clicking Shift and placing the sign then typing [Private] <name>
2. Shows in chat: 2nd or 4th line invalid. And the [Trade] changes to [?]
Fix: /lookup <Item that's invalid> you'll get a list of tradeable items. (Sometimes you have to use the item id instead.) See here for those: http://www.minecraftwiki.net/wiki/Data_Values OR, use /l <item> and the number next to the item is the item ID
3. The sign says "Neytiri :D"
Fix: don't click the chest, place it in front of the chest
