Haggling is one of those useless skills no one bothers training. Let's have it, instead of being something you use actively on a shopkeeper, give a passive bonus/malus to player sales/shopkeeper prices, with no particular chance of failure. In this way it would work somewhat similarly to the passive bonuses given by Dodge and Athletics... and while I doubt many people would bother leveling it anyway, given that gold is very easy to come by, at the least it would provide real and tangible benefits, particularly in the early game, in a way people could see. Sounds fair to me!