Maybe instead of having an NPC handing out a "summon NPC" scroll, you could take one of those empty buildings in the Harbor and in the Marketplace and make them into a guildhouse? A "hireling guild". You could go in and speak to any of the NPC's you want, actually see them and interact with them in a "lets work out a deal" sort of way, and they say "Ok, lets sign a contract" and then it appears in a loot window or something. That way it would feel a lot more like you were actually hiring a real person and not buying a piece of loot.