A good realtor is worth every penny you pay them and in addition buying or selling your home will:

• Listen to and help you manage your expectations.
• Make sure you get a knowledgeable and thorough home inspector.
• Keep you from getting the shit sued out of you for one of numerous mistakes.
• Make sure you fully understand the giant pile of paperwork you'll be signing.
• Have O&E insurance so if they fuck up the paperwork, it's on them and not you.
• Go to bat for you if you're being discrimated against in any way by banks, buyers, sellers or landlords (all of which are rampant).

The problem is that a lot of realtors are good at "shaking hands and taking names" and terrible at everything else or they're just plain unethical. Unfortunately, that's the vast majority of realtors in my experience.

Source: wife is a realtor who tells me all kinds of "you'll never believe the shit [other realtor] tried to pull today" stories.