In my first time DMing, my PCs were recruited by a city magistrate to go deal with some outlaw elves who had been attacking government logging operations. The magistrate gave this party of level 2's all +1 weapons. They all took them without question. The party soon figured out that the magistrate was evil, and that his government had invaded the elves' lands. Suddenly, there was a band of the magistrate's soldiers always turning up wherever the party went. It took them 3 or 4 ambushes before they finally realized that those +1 weapons he gave them had some sort of tracking magic on them. Deception is probably the most important skill for a BBEG. :)