I actually make a lot of profit by selling in small stacks at a premium price. People have things like two-star foods listed in stacks of 20-50, and things like lumber listed in stacks of 99. Who really needs 50 food or 99 lumber? Most people don't want that. They want the 1 lumber they need to finish the item in their crafting log/levequest or 2-5 food for raid day. So I list food 2 at a time at 500-1k over the going price and they sell like crazy. The same goes for lumbers and the like - I list in stacks of 5 at an increased price and they sell like crazy.
It requires a lot more micromanaging my market listings, but it makes good money.