This story's a bit different. Usually we name companies when they've done something wrong. And while I do feel the company Leona used charged her too much, I don't feel we're justified singling them out. They may be the most expensive company, but they let Leona know the price before hand. And there's no industry standard, so it's a buyer beware situation.
It's hard to know if you're getting ripped off or not when it comes to hiring an ac/heat repairman. Some charge you a "trip fee" and most will charge a diagnostic fee to find out what's wrong with it. Doing that with several companies in hopes of shopping around just doesn't make sense. That's why you should use a reputable company - which has been recommended to you.
But as for the bigger jobs, like buying a new ac/furnace, I would recommend shopping around. Keep in mind, cheaper does not always mean better. That's why the "Air Conditioning Contractors of America" have put together a checklist to help you determine which company to go with.