Are you hiring a contractor to provide services?  Make sure you ask to see the following insurance certificates;  Workers Compensation, Automobile, and Liability.  Also verify that the contractor utilizes employees (W-2 wage earners) rather than subcontractors (1099 workers) as your liability is much lower when the contractor has employees that are covered under the abovementioned insurances.

Source: http://www.entrepreneur.com/article/225773