The onslaught has begun when it comes to inventory. With the announcement of Mists of Pandaria released in September, players are emptying all their reserves into the market. They do not want to get caught with their proverbial gold pants down.
This is where your training and experience will come into play. As markets start to become less viable, there will still be demand for some items. Raw materials will still have some market acceptance as players finish off their crafting queues to reach their maximum level. Inventory dumped in one area can easily become saleable items now, or later down the road.
My personal favorite is the Jewelcrafting area. Players are dumping their extra gems that were produced with the Elementium shuffle. Leaving inventory at low costs and driving down prices.
But remember, you have an army of new players that will need leveling gems. They will also want to use gems for turn ins for their Jewelcrafting dailies. Plus those gems are easily converted into materials that will still sell if you have access to an enchanter. Even the lowly Zephyrite will be useful for turn ins as Mists of Pandaria begins to mature on the servers. So instead of just vendoring everything or selling at a steep discount. Look to see what can be converted or the chance later on in the market.
Volatiles will still be needed as MOP continues on. Players will want to level their professions, and make an occasional item. So investing in Volatile fire for 2g a piece could easily double your investment down the road. Gold Goblins never turn down a chance for profit.
Also look for guild banks to come up for sale. Players deciding not to return to the game after their wowcations. Raiding guilds no longer viable, jumping on a quick buy of a guild can give you a large amount of items to profit from.
Where markets are slow to buy, there is a trickle down for large items that can continue on through the expansions. Mounts, pets and vanity items become big sellers as players sort out space in their banks, and look to entertain themselves.
Keep your goblin eyes open, and be on top of the markets.