Do not automatically accept the contractor with the lowest price.
First, make sure all bids are based on the same set of service and equipment specifications. Discuss the bids in detail with each contractor and make sure you understand the reasons for variations in price. A higher price may be your lowest overall cost if the materials used are of higher quality or the work is more complete.
Beware of a bid that is substantially lower than others. It indicates the contractor has made a mistake or is not including all of the work (and/or material) quoted by competitors. You are sure to have a dispute with a contractor if you accept a low bid based on an error or misunderstanding.