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Arenanet handed us an incredible gift when they created the "Top Traded Items" list. It's the first panel that appears when we open the trading post, and the most important column (the top 10 traded items) is all the way on the right.
These markets are always incredibly fast moving ones, providing impatient flippers with a place to put their gold. At the time of this writing, I was flipping green logs 250 at a time from 50 copper to 63 copper. The profit margin fluctuated between that and 51/62, which is still a one copper profit per item. All I had to do was place a 250 item buy order, work on other trading post activities, then check back in 30 seconds to grab the sold green logs and relist. Within ten seconds those were sold as well.
Sometimes the market would shift (like I said before down to 51/62) and then there would be a 5-10 minute pause in the action. This is why I never do more than 250 for these items, as they are incredibly volatile. All in all I did this around a dozen times, for a profit of around 1 gold 20 silver. It's just one more easy method for those of you who need something to do while you wait for more expensive buy and sell orders to finish.
It's really important when playing these markets to pay attention to walls. If you see a listing below 500 that is NOT a wall in the case of the top ten traded items! You can comfortably place your buy/sell listings past these low stacks of items. You're more interested in finding the real walls, which usually are several thousand items for the same price. Don't always assume that the lowest price is actually what you want to go with, so I highly suggest that you click the item on the trading post to see all the listed prices when you're going to select a price to sell at. Otherwise you're operating with just the "match lowest seller" price. One trick I use is to right click on the item in my inventory and choose "buy more" in order to bring up the trading post and see all the listings. You can't do that from the sell tab.