This dragon, though ancient, powerful, and dangerous, is a plot device to get the main plot rolling, more important for something that happens while the dragon slaying is going on than for itself. (Sometimes even dragons have to play second fiddle.)
So the slaying is constrained by its purpose. It has to involve some organization, so that an idiot can attempt to interfere seriously enough to hinder if not stopped, it has to involve knowledge of dragon slaying so our hero can keep control of it, it has to involve a number of people because I don't want our hero to be too high level.
Starting off with the notion of tricking it with a lure of gold. An illusion might suggest that its owners were fleeing thus giving the dragon a reason to not suspect it -- but our hero has to shoot down the notion that the gold be an illusion as well. And the next step is figuring out the attack once they lure the dragon in place. They can get it somewhere, but once there, they must kill and not trap. I wonder if our hero will have difficulty getting magic into the hands of those who attack. Probably going to have some difficulties with the notion of pressing the low-born into duty.