Typically in game need systems of control in place to prevent cheaters, if the inventories are stored externally this might present an issue? Also I don't think

Typically in game need systems of control in place to prevent cheaters, if the inventories are stored externally this might present an issue? Also I don't think that trading system itself is that huge of an investment so much as the management and interface of it all which would still need to be developed so... seems dubious to say the least.