Stress
You know why most jobs are stressful? Because sometimes human beings can be pretty unreasonable. Sales-related careers are full of stress. You have high goal numbers to reach, people who won't return your phone calls, and clients you have to hound and pamper in order to keep their business. At times, everything falls into place. At other more frequent times, no matter how hard you work, things just don't go your way.
Ultimately, your job as an energy broker is to convince people to buy a specific energy package. That means you'll likely have to bend over backwards from time to time in order to convince whatever business or city with whom you're working that what you're selling is the absolute best.
That said, regular people are usually pretty skeptical of salespeople—and usually for good reason. Keep in mind that you'll have to lose sales, anger clients, and generally expect everything to go wrong in order to learn how to be a decent broker. It'll be stressful, to be sure, but you'll find yourself growing with every failed account.