Alternatively Speechcraft (and maybe Willpower) could be used to determine if the attempt to haggle is sucessful (or if the customer's attempt is resisted), Merchantile (and maybe Intelligence) could be used to determine how much the price has changed and Luck (and maybe Personality) for either an additional amount of septims or an extra sale. Using these attributes on top of skills favors mages so I'm not sure if it's a good idea except for Personality. Beggars could occasionally buy cheap clothing too. Maybe a 0.1% chance for them to buy the most expensive item you have? Nobles should have a low or zero chance to buy food, drinks and cheap clothing. For simplicity, have them not consider buying anything below a certain price since it's most likely items that they already have plenty of or easy access to. The Imperial City has lots of potential customers but they are also spoiled for choice. They should get a bonus to haggling there.