Workers Compensation Insurance protects you if a worker is injured on your property. Liability Insurance protects you if any of your property is damaged. It's common to ask a contractor for their insurance agent to provide a certificate of insurance or to be an additional insured on a large project. (If their insurance is not up-to-date YOU could be liable.)
GET IT IN WRITING
All warranties and estimates must be in detail. It will help protect you as a consumer and avoid misunderstandings.
Does the company stand behind warranties? Did the contractor listen to you when there was a problem? Do they actually show up on time? Would previous customers use them again? If they cannot provide references, there's a reason why!
HOW LONG HAS THE COMPANY BEEN IN BUSINESS?
Warranties are only as good as the company providing them. If they go out of business, in many cases so does your warranty.
DON'T SIGN ANYTHING - UNTIL YOU FULLY UNDERSTAND AND AGREE.
Be sure to ask questions and clarify everything in writing. Taking time to ensure that you and the contractor have clear expectations will ensure a smooth and problem free project.