No doubt you are seeing the inflation results of 3.5 billion people having more time at home.

The main tip that can be given is play the game and do stuff that results in crappy loot that can be vendored or is in demand on the auction house.

Most people with their gold hoarding have done the hard yards of playing the game to figure out what collection method suits their play preferences, and what monotonous tasks they can be bothered with, and any special locations they keep that info to themselves, just in case a million others come along to "their" spot, and thus exploit and expose it.