Talk with others who have had work done by the contractor about the company's capabilities and quality of workmanship. Make sure the contractor has a permanent business location and a good reputation with local banks and suppliers. Incorporate any warranties, guarantees or other promises in your written contract. Always insist on a written contract and written change orders. Be specific about starting and completion dates.
Some delays are unavoidable and beyond the contractor's control.
Beware of an unusually low bid or low advertised price. If a contractor cannot pay for labor, materials and overhead, you are both in trouble. Although reputable builders sometimes offer special discounts for advertising purposes, watch out for contractors who offer unusually low prices in exchange for advertising. Protect yourself by asking the contractor for a list of previous clients who also had been offered the special rate in exchange for advertising considerations. Call the references and ask them if they received the promised quality workmanship and special rate.