I like to crash the 16 slot bag market periodically. This is mainly because I couldn't afford the bags when first starting on my server and I've never forgotten. So I buy all netherweave cloth I can find and make the bags, undercutting everyone else, then undercutting myself till the price is almost half of normal.

I don't outright sell for much less because they would just be bought and reposted at higher. Undercutting over and over seems to prevent this.

Even though I make lots of gold with my bank alt I consider myself as an asset to the buyers. When prices are too low it can cause supply to dry up and then everyone loses. So I buy when to low. When prices are too high I undercut those people and clean up.