A note about big patches
In the days immediately before a major patch like 5.4, players are obviously stockpiling like crazy. It's natural to be inclined to reduce sales, hunker down, and build inventory. That means that prices on some mats will spike - so don't be afraid to do some selling in advance of the patch if conditions on your server support it. Sometimes you can make some very nice profits a day or two before a patch, simply because you're not dealing with hordes of competitors.