So much truth in this. I have made mountains of gold buying up cheap mats in small stacks and relisting in bigger stacks at double the price. And yes, I have seen stacks of ore/cloth/leather sell at 1000g for a stack of 200 when there are 1000 singles listed at 2g each.
People who list large quantities of singles are cancer.
I agree with that. It costs me less than 100g (plus my time) to make a frostweave bag. If someone else has listed a few for 500g and these might sit there for days. I will sell for 399g and they will move like hotcakes because the buyer sees a ~40% discount (yes I realise this is only a 20% discount, but many people just see 300 instead of 399).
Also I have known people who will use 2 alts to play the auction house. They will list a dummy item at an absurd price with their first toon and then list the same item a lot cheaper (but still expensive) using a different toon. It creates the illusion that the lower priced item is at a good price.