There should be a new job called Trader.
You buy things from AH and re-post them at much higher price for a marginal profit. Each time you make a sell, you gain experience. And, the job provide you with percentage bonus gil and AH fee waiver as you level up!!

Heck, traders are already in every MMO games that have an auction house running. I'm sure there are people already running this virtual job! Despicable? Smart? Your choice.