Next, be sure to compare apples with apples. Consider offering your top candidate a flat fee to spell out each step and material so that others can bid on the same thing. "Generally, materials account for 40 percent of the total cost; the rest covers overhead and the profit margin, which is typically 15 to 20 percent," says Tom Silva. And, yes, says Steve Miller, owner of HomeProHub, a home-improvement consulting firm in San Jose, California, it's okay to negotiate. He recommends doing it by e-mail, which puts everything in writing and helps conquer fear of haggling. Even top pros have dry spells and may lower a bid to keep crew members busy, he says. Keep one eye on the calendar—winter months are often slow—and be flexible. "Life happens to pros, too," he explains. "Divorces, taking kids off to college. So stay in contact, and later, if he loses a job, he can pull up your e-mail.