Without going into specific numbers, when my wife and I put our home in Glendale, California, on the market a few years back, our realtor recommended a figure that just seemed too low to me. We decided to list it 12% higher, a hefty chunk when dealing in home price figures.
As it turned out, the home went for much more even than that, selling for 18% more than her original figure. Had we simply trusted our agent, experienced and knowledgeable as she was, we would have left tens of thousands of dollars on the table. We got that one right, but many other people don't.
Use recent sales in your area as comparisons, consider a second or third opinion from other agents, and consider how much you have invested into renovations and maintenance over the years — you may know your home's value better than a professional realtor thanks to your firsthand experience living there. (Also, note that listing too high can lead to repeated drops in the price, signaling to buyers that you're desperate to sell and giving them leverage in the process.)