But that’s only 1/2 of a real auction house, which also includes a buy/bid side, where people also post what they want to buy and the price they are willing to buy it for.

Markets are liquid when the bid/ask coincides in enough volume that deals get done and the market is constantly gets cleared, and illiquid when that does not occur.

That one change would make the WoW economy much more interesting, imho.

A deconstruction option that returns raw mats would give the ability to skill up using the mats as well as providing an alternative to lets de that item and get another void crystal.
Surely it would make sense that a blacksmith could take a sword or plate chest and smelt it back into a few bars of metal, perhaps not as many as used to make it but some at least. Or a tailor recovering mats from a robe.

Or another approach is to add a research ability, much like glyphs. A big epic gun drops in toc, an engineer uses research on it, the gun it taken to bits and destroyed, but you receive schematic 1-a or 1-b etc from gun, if you combine all 8 schematics (ala darkmoon cards) you get blueprint and you can learn to make this item.

The tradeskills in wow could be expanded to provide much more functionality than they currently have, especially at end game where the only tradeskill used in a day to day way is the disenchant function of enchanting.