Never sign a work order until the damage has been assessed and the estimate has been fully reviewed with you.
Never pay anything before the job is completed
Always use a licensed contractor, why? You can be held liable for on the job injuries or insurance. Not complying with city or county codes and correcting problems are all your responsibility when not dealing with a licensed contractor. You can even be held for his/her illegal acts. Hiring an unlicensed contractor is risky business.