Get at least 3 bids and ask for references of work the contractor has completed in the local area.
Contact the people provided as references by the bidding contractor and ask questions that will help you decide whether the contractor you are considering hiring will satisfy your needs. This takes time, but saves money and aggravation in the long run.
Don't pay cash, don't let the payments get ahead of the work completed, and don't pay the full cost of the job up-front.
An additional companion resource - the "Home Improvement Guide" - is also provided to public agencies and the public to put NCBE members in contact with prospective clients.