MoGPvt.Hile's idea is pretty cool, and there are revenue forward ways to make it work, ergo, more of an 'eBay for Guns' than a Craig's List... The answer is in making all parties winners -- which from the current design of the leveling system, scoring system, and Developer obstinance to criticism seems unlikely to be welcome or understood i.e the Developers or Ubisoft feels someone has to be a punished substantially to gain something and there has to be a 'Looser' in every transaction in the game... But just one simple illustrations of how revenue forward market design could work in a resale system :
The Seller on the 'Weapon Bay' only makes a little more on the sale then giving it up for sale in the game automatically, the down-side is you wait a little longer for the sale to complete...
All weapons sold on the Weapon Bay are 'used' so performance is degraded in some regard that the 'Weapon Bay' documents. The degraded performance can only be 'upgraded' with real currency credit, not RP.
Buyers are able to purchase weapons more advanced than their current level, but, they must pay for the transaction again in a balance of real currency, the cost is less then the 'new' weapon, but it is able to be purchased 'out of turn' (before the Player levels to it)...
How everyone 'wins' in this illustration should be pretty obvious: the Seller is able to move a weapon for more RP; the Buyer gets access to weapons faster then he could vial leveling, and outright purchase through the Game; Ubisoft gets real revenue from a transaction that otherwise would not exist, that does not compete with the existing revenue model, and grows their transaction model... However making money and sound business practice translates to 'the sound of f@rts in the wind'' in the French spoken at Ubisoft -- if one takes a look at their financials...