As an alternative to the endless begging for an "auction house", why not try something different and implement a Trading post\Items wanted board to allow people to request items.
Instead of having this designed for sellers (who already have zone chat and guild traders), it would allow players to be able to place a request for between 1 and 5 different items [I would suggest 1 item at a time], and for others to be able to supply these items for them (And who knows...Maybe a "daily" quest could also be supplied at a later stage).
For example, we have a player who (for some unknown reason) wants a CP160 "training" Spriggan's restoration staff. This would allow them to place a request at the trading post/wanted board, along with their offer price and a % buyers fee (deducted from their account and held until item offered or request removed). others could then see what items are wanted, and potentially decide to either request the same item, with whatever price they wish to pay for it, or sell the item to whoever has the highest offer for it (Or request a completely unrelated item). Payment would be received instantly, with the item arriving in buyers mail in the same way as items from a guild store.
This would both allow an extra potential gold sink (both through less money entering game via bottomless gold-source of vendor and the % fees applied) as well as making it easier to acquire those "unusual"/"worthless" items which rarely make it to guild stores as their value is considered too low to be worth listing. In addition, all players would then have the ability to sell items (maybe with a daily/weekly cap similar to that of fences) removing, or at least decreasing, the constant demands for an "auction house", while limiting the impact on the current guild trading system.