Auction house (or another suitable name for such an establishment)
After reading this thread:
http://fodev.net/forum/index.php?topic=21325.0I had a think.
At this location a player could bring his items, and place them up for sale in the care of NPC traders.
Prices for each item would be dependant on a predetermined value for each item, the player could put his items up for sale with a 10% difference in price either way. This way if there is alot of supply for the item you are selling you could undercut some traders a little by selling a 100caps item for 90caps, or puch the price up to 110caps if there are no other sellers for the item. The limit on the price for each sale would deter a group from buying all of something and reselling it at a much inflated price (which, if done enough times on a regular basis, would render this place rahter useless)
Via some fancy programming (which can, and has been done in at least one other game)... the predetermined price can fluctuate. If alot of people are selling one item for a low price and they arn't being bought, then the predetmined value with gradually get lower. If there are few of an item being sold, but at a relativy high price, then the value will increase over time. Eventually the value of items will reach a balance, in theory (barring flooding of a particular item)
As to how it works, you could simply bring your items to the location and engage in some dialouge to put up your items.
After (insert time here, open to suggestions, 2 days?) if your item has not sold you can collect it at a later date for a fee, on those lines if you item does sell you can come collect your caps as you see fit, again, for a fee. Either way, the NPC's will be taking a cut even if your item does not sell as they have to make money somehow to pay their guards.
Speaking of guards... there should be many. A place like this would be a prime target for factions to attack and in my opinion it should be VERY hard to take and hold this area considering the quality of people and equipment that can be purchased with all the cuts they are taking on sales.
Traders would still have a place, there are several options for them.
One is to simply ban certain items going up for sale so manually selling them or trading to NPC traders are the only options.
Another could be having certain items only spawn on certain vendors so those vendors remain useful to some degree, possibly combine that with the banning of those items from being sold at the auction house.
Also after some time certain items will have a much larger supply than demand, so it would be more profitable to sell to a vendor than put it up for sale or demand would infalte the price of some items so purchasing from a vendor would be preferable.
Another way to make vendors remain useful are mini-quests, such as collecting X of something for a small cap reward and karma boost to replenish a vendors stock. The items needed for these could change from day to day and vary from vendor to vendor depending on what they mainly sell.
Problems (and fixes), suggestions, etc?