Screenshot taken a few minutes after the buy orders were placed.
This past weekend I decided to flip 8 non weapon/armor items in order to show just how much gold you could make with a small number of items on the trading post. I logged in to place the buy orders, then logged in again that night to place the sell orders. Took about 20 minutes total to find the items. I tried to pick a wide variety of items but didn't spend too long looking for them.
The items were purchased with buy orders at:
Mystic Coin - 1 S 98 C
Small Claw - 14 C
Wool Scrap - 32 C
Salvagable Metal Scrap - 60 C
Pile of Metal Scrap - 57 C
Crystal Sliver - 3 S 59 C
Glacial Sliver - 1 S 95 C
Molten Sliver - 5 S 20 C
Profit on these items ranged anywhere from 1 to 50 copper. I bought on Saturday morning and sold on Saturday night. For the more expensive items, I only placed a buy order of 25, but the inexpensive ones were in the 250-1000 range.
I invested 8 gold to get these items and made...
So that's a 7 gold profit in less than 30 minutes of total play time! Taking off the time to find these markets, it was really only a couple of minutes! So each day now I have been using these same markets and making around 5-10 gold. All I do is log in when I wake up and right before I go to bed. ANYONE can do this, which is exactly why I tested it. But there's a catch...
The biggest thing I did right with these items was selling intelligently. I didn't go by the lowest price and subtract 1 copper, but instead looked at the listings in order to find where the next "wall" was. For the wool scraps, I saw that there was a wall of items listed at 42 copper, as in thousands of wool scraps. But then there were like 200 listed at 40 copper. I just posted for 41 copper knowing that the other 40 copper one would be bought out eventually. This was also true for Salvageable metal scraps, but in a much bigger way. There were tons of 1 or 2 buy orders a copper apart, going from 70 copper all the way up to 90 copper. But then there were thousands at 91 copper. So what did I do? I posted at 90 copper knowing that the others would eventually be bought up. I didn't buy them because it would have resulted in a loss after fees, but undercutting those items would have cost me big time! In fact, I would have lost gold in the process.
Instead of waiting for the cheapest item to be worth undercutting, choose the lowest "wall" of thousands of the item and undercut there. Your items will sell overnight, and this saves you a lot of time waiting for the right moment to sell.