Do not automatically accept the lowest bid. In fact, you should beware of any bid that is substantially lower than the others. It probably indicates that the contractor made a mistake or is not including all the work quoted by his or her competitors. You may be headed for a dispute with your contractor if you accept an abnormally low bid. It is also possible that this contractor will cut corners or do substandard work in order to make a profit on the job.
Most licensed contractors are competent, honest, hardworking and financially responsible. A responsible and informed consumer can work more effectively with reputable contractors, and can avoid being victimized by unscrupulous or unlicensed operators.