We Need More Writers!
I get a lot of emails from people specifically stating that flipping isn't working for them because sellers are constantly undercutting their buy orders. Think for a moment, is this physically possible?
Yes, it is possible for people to undercut you after you place a sell order.
But is it possible for prices to always decrease? No, at some point they must go back up. So if you stick with it for more than a few tries, you should eventually see success. Keep in mind that when you're winning buy orders, the price tends to be going up, so it's also a good time to sell. When you're not winning buy orders, the price is going down, so you wouldn't want to win right now anyway!
Best defense against this is to start figuring out the "normal" price for an item. Then you can take one look and decide if it's time to buy or sell. Most people start off by just placing buy orders at the current price of an item they heard about on this blog. What if the price is high today? Then you're going to wait forever for buy orders you really shouldn't want in the first place.
Start writing down the price of a tier 1-6 crafting material of your choice every day. Eventually you'll have a grasp of what range of prices it can have, which will help you decide on buying versus selling every day. Don't just go onto the trading post presupposing that today is a day to buy!