The following are possible enhancements to such an auction house system.

Auction house accounts:
A character can create an auction house account by speaking to an NPC at the auction house and depositing gil into the new account. This yields the following benefits:

a) An Auction House NPC linkpearl is supplied to the character
b) Bids can be made via this linkpearl, but only using the gil funds currently on account
c) For a seller, current status of an auction can be checked via linkpearl, and the auction can be closed via linkpearl. The resulting gil is place in the character's account
d) Depositing/withdrawing gil must be done in person
e) Initiation an auction must be done in person, to supply the item
f) Retrieving an item won must be done in person

Alternative Listing Fees:
It has been pointed out that having a high listing fee would likely make the auction house system the exclusive province of 'end-game' players, and would not enhance the playing experience at all for low and mid-game players.

To address this, the following alternative fee listing system is proposed:

Listing fees are determined by item availability within the market areas.
When an item is listed within the auction house, a check of all market areas is performed. The initial listing fee is 5000 gil per item found within the markets, with a maximum fee of 100k. This system explicitly provides deconfliction of the the proposed auction house with the market areas, and provides for lower rank crafters and buyers to participate in the auction house.