I might be missing something, but all I see is a another needless restriction. I don't see how this would benefit the game. If you own something, it's yours to with as you please, including selling it.
Buffalkill - the abuse comes because it is a way to transfer money to units on the battlefield, far from their own cities.
An extreme example of this would be a single "runner" who comes out to the siege party with 2000 gold & just does a series of transactions back and forth of the same item, with the true purpose of distributing gold so that nobles don't have to break off the siege to refit as the game intends for them.
