I once played in a PVE server where buying and selling items were a norm. They have a shop system in-game where you could buy items from. The prices in the shop are usually very high, for example, an alicepack would cost 10,000 Zeni (the currency). Thus players would always bring down to price to about 4,000-6,000 for them to be able to sell the item.
In this case, Freezzer has a shop AND a market which is really cool. However by observation the market is not really active and it's quite surprising because I really love this open market idea. I'm not sure if a lot of the players know about this but having it in the server broadcasts might be helpful, stating something like: We have a market where you can buy/sell items from each other in an organized manner. Overall just establishing and encouraging the use of the market. Perhaps there could be some kind of bonus if a player uses the market?
I could print a message everytime they use the regular /buy /sell commands. 
The dollar notes were basically added into the game for this sole purpose, so it would be great to have something like this
Can't you craft dollar notes with clothes? 
Can't you craft dollar notes with clothes?
No you craft dollar notes INTO cloth
