Did that merchant rip you off - but you took it because you're broke? Sell 'em vender's bane and get back at the cheap good for nothing slob. The trade house in Seyda Neen has a new surprise for you - check it out next time you're in town (don't worry Arrille will respawn after awhile).
Be careful - This patch should only be used for justifiable homicide - killing merchants can be a dangerous strategy.