It isn't a matter of playing on fears, it's a matter of surfacing inherent risks and potential issues a customer may encounter that they may not have already taken into consideration.
It's really all in the delivery and approach, however. If you're being a manipulative douche bag, that's probably going to come off as pretty obvious to a customer, and you screwed yourself.
Every customer, every set of circumstances, require a different angle. When it comes to security products, you don't want to sell too little, but it's easy to sell too much. When you're the guy who raises relevant issues your competitor either didn't want to bother himself with asking, or didn't even think of, you put yourself in the forefront of consideration, and sales are closed.