Along with the other top questions you want to ask during the process of hiring a contractor, you should also request itemized price estimates from each candidate. After you receive these, it's best to examine each one carefully, paying particular attention to any that seem too high as well as too low. Estimates that fall in the shallow end of the pool can be a red flag for a hasty job that won't leave you with a quality finished product. If an estimate seems a good deal pricier than others, that could mean the other contractors were missing some core obstacle involved in completing the project and therefore didn't set a high enough estimate for a proper job.
You'll also need to negotiate the payment schedule and determine how any surprise expenses or potential change orders will be factored in. Planning the payment schedule needs to be a give-and-take, but the more you can negotiate to keep in your pocket for as long as possible the better: You never want to pay for more than what you've gotten at any particular time. And don't forget -- don't sign that last check until you're completely happy with the completed project.