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First, realize that the bots aren't the ones undercutting you. Those are real players, and the shear number of them is due to the fact that you're playing against the entire world. That's right, it's a global economy!
You can either take this like a punch to your face, especially that undercut that sent you searching online for ways to deal with undercutting, or you can take some advice from yours truly.
Having so many players in one place is a good thing. It means faster sales, and more opportunities for profit. When that mean person undercuts you by a copper, let him! When thirty people undercut you by a copper each, let them! The marketplace will take care of those individuals and eventually get to buying yours.
The majority of players enjoy Guild Wars 2 at night, and since most are from Northern America, that time zone is what you should use as the measuring stick in this post. So if night for you is a few hours different from this part of the world, then you have to adjust accordingly with your playstyle.
What does it matter when players are on? Well, what if I told you that prices across the entire trading post go down incredible amounts during the week, and then they go up an extreme amount during prime time on the weekends? That is an opportunity to flip items, and a massive one at that. Crafting materials and ingredients, the ones getting sold by the thousands every minute, are where these opportunities lie. Like flipping copper ore. The trick is to always use buy outs and to be patient when selling.
So next time someone undercuts you, realize that it's a natural part of the economy, and you're too smart to get mad about it now.