Collectors could be used as the way to balance the economy. As it stands right now, you give a collector 3+ items, and they exchange those for an item of use. Sales through bartering. But why do they collect the items in the first place? Why not have them actually do something with those items.
Example: Marchena collects minotaur horns in the desert. For 5 horns, you get a piece of armor. Why just leave it there? There's no economics involved. The collector doesn't make a profit - what are you going to do with minotaur horns?
So, what if Marchena uses minotaur horns to make clean max-damage hornbows. Which she sells for an amount based on how many minotaur horns she receives against how many horn bows she sells. To pull a number out of my ***, since she takes 5 horns anyways, lets say she uses 5 horns per hornbow. The price of a hornbow will be, for the sake of this arguement, 5k gold. Now, the more horns she receives, the more bows she has in 'stock', and the price of her bows begins to drop. Then people start to buy the bows, and the price begins to increase.
How does this affect the economy? Well, if the bow is being sold for 5k gold, people will charge less. Perversly, people might instead sell minotaur horns at 200g per horn - 1k gold for 5, which is exchanged for a hornbow, with a net savings of 4k. Now, sure, if a bow is selling for 5k, people will sell horns for 1k. But if there are more horns being exchanged to her directly, the bow price drops, so the horn prices drop, and then it becomes the buyers perogitive what to purchase - horns, or the bow.
And if there's another collector somewhere else also taking in 5 horns, but to make... max clean bone staffs... then the market really takes off, because buying horns gives the buyer a choice of what to exchange for, and the prices on all 3 items will fluctuate.
So, lets take it one step further - rare item collectors. We already have rare materials traders, this would be something similar. Lets put a rare collector in the Oasis. This specific collector takes in major runes - an item that's currently really depressed in the economy - nobody wants them. For 5 major runes of a given class - lets use swordsmanship runes in this case - the collector exchanges for an item relevant to that rune: umm... let say max damage dragonsword of wounding, for example. This pushes the price of major swordsmanship runes up, cause a lot of people would want that sword.
Now, the collector has to make a profit somewhere, right? So, this collector sells superior runes. And their price is dependant on how many superiour runes he sells, against how many major runes he receives - if no one gives him runes, then the sup runes would be upwards of 50-60k (as a price out of my ***, again). But as he receives more major runes, the price of superior runes drops until it's at a level where people will purchase them... and then the price rises until he gets more majors. Eventually, it will stablize as a price the market can accept - until the build of the week comes out, and a run is put on those runes. Ah inflation.