I REALLY love how the market system works on Guild Wars 2. First of all, you can buy and sell anywhere ("mail pigeons" appear doing the work of sending your items/money away), you just have to open the market interface and do your thing. If you're buying, the items are sent to your "inbox", but you can only retrieve them on an NPC that is available in big cities and some settlements. If you're selling, your money will be available to retrieve the same way. (Oh, did I mention money is shared with all your toons in the same account?).
Then, the market is perfect, imho. When you're trying to buy something, they'll always allow you to buy from the cheapest seller first (and you don't need to buy all the stack of items, you can buy some if you need to). You can also place a buying offer, set your price, and wait for people to sell it to you.
When you're trying to sell something, they'll always allow you to sell it to whom is buying for the highest price first. You can also place a selling offer, set your price, and wait for people to sell it to you.
Marketing is a serious business in GW2 and it's also fast and convenient.
I fully agree. The trading system in GW2 is great, especially the marketplace/auction house. The only thing you need to consider is if there will be bind of equip, bind of pickup, soulbound items ect. I personally would like to be able to trade everything and I mean absolutely everything.