Vendor Resale--The Best Way to Make WoW Gold

By far the quickest and easiest way to make gold is vendor resale, which basically means you take items that you buy from a vendor and re-sell it on the Auction House for a profit. It is easy to gain at least double your money (100% profit), but I sell items all day long for 2700% profit. How is this possible? I take an item(ie: Formula: Enchant Chest - Minor Mana) that costs a mere 3 silver,