Many of the fedual nobles were not sharp managers and were always short of cash. They could not easily just increase taxes, as these were set by custom and could not be unilaterally changed without risking unrest or condemnation from the local clergy. The custom developed for nobles to sell their rights and privileges (as well as their land, if they were in dire straights) for cash. Towns were quick to take advantage of this, as they had access to more money and could do more with "freedoms" (from taxation) purchased from their feudal overlord.