I used to do something similar in WoW, but less on the "know every item in the market", mostly just a few crafting subsegments. There was a Auction House plugin

I used to do something similar in WoW, but less on the "know every item in the market", mostly just a few crafting subsegments. There was a Auction House plugin that let you monitor/record prices, so it was easy to learn the normal price/supply of materials. Especially for things that didn't trade at a high volume, it was easy to see that some uneducated player had listed a single jewel at .5x the actual value and then auto-buy and flip it for 100 Gold profit. As OP says, I do miss that feeling of completely understanding something and being able to ruthlessly exploit it.